I'll post this for future reference by anyone planning on getting support from Canon on this issue.
I contacted Canon tech support in the UK since the printer was apparently never sold in the US. What I asked:
Trying to help a user with an LBP-810. They upgraded to Windows 10
(don't know if it is 32 or 64 bit version). It appears that the latest
driver Canon offers is Win 7 32 bit. Is there any way to use the
printer with Win 10? (Some type of compatibility mode in Win 10? Win
10 driver for a similar printer that will work, even if limited
functionality? Load the driver in a Win 7 32 bit virtual machine
running in Win 10? Driver in CUPS that would work in a Linux VM?)
In fairness, it probably isn't realistic to expect a manufacturer to suggest a solution in which their product would not perform as intended. And since they're in business to sell printers (or perhaps more accurately, to sell mechanisms for which they can sell expensive supplies), and it's expensive to continue to support ancient hardware, few companies will help you make their very old stuff limp along forever.
That said, here is their reply:
Thank you for your request and for contacting Canon.
We are sorry to inform you there are no drivers available for your
LBP-810 with Windows 10.
To explain this lack of availability we would like to provide you with
some additional information regarding Canon's policy towards the
provision of drivers for new operating systems.
At the time of launch of a new product, Canon generally provides
drivers so that the product in question will operate on all existing
and known future planned operating systems.
When the launch of a new operating system is announced, Canon reviews
the existing product range to see which of these products can be
considered for the provision of compatible drivers.
There are many different factors that may influence this decision.
These can include (but are not limited to) such factors as the
technical compatibility between the new operating system and the Canon
product, the cost of driver development, the cost of supporting
utility software product updates, the issue of certification of the
developed driver by the operating system in question, the expected
lifetime of the Canon product and costs associated with quality
assurance.
Canon respects the right of its customers to decide to upgrade their
operating systems and we attempt to make it clear at the time of
purchase which products will function on which operating system.
Furthermore, Canon always advises its customers to check the
compatibility of their associated Canon products prior to the upgrade
of an operating system. To this purpose, our consumer helpdesk staff
are always available to assist customers with such enquiries.
We hope that the information above offers enough explanations with
regards to the unavailability of the updated driver that you need.
Once again, thank you for having provided feedback on this matter. We
appreciate the time and effort it has taken you to do so.
Yours sincerely,
Michael Robinson
Canon Services & Support
So bottom line, you're still in the same place looking for an external solution, but you now definitively know that this is not an avenue to a solution.
What make and model of printer is it? In my experience the Win7 drivers have tended to work in Win10. – Burgi – 2016-03-02T10:52:35.990
Model is Canon LBP-810 – EngineerSpock – 2016-03-02T11:18:07.043
I don't want to post this info as an answer because I have no way to test it, but: 1) This issue with your printer dates back 6-7 years. I found a number of threads with suggestions, but reports of no success. 2) It looks like the Win 7 32 bit driver simply won't work with 64 bit OS (even Win 7); you don't indicate whether Win 10 is 32 or 64. 3) The only promising avenue I found was using the XP driver in XP compatibility mode. There were mixed reports of the availability of XP compatibility mode in various 32/64 bit Win 10s of different versions. – fixer1234 – 2016-03-02T20:18:25.913
BTW, the reports were pretty universal that Canon was unhelpful. When people got a response at all, it was that the printer was too old (and this was years ago), and to buy a new printer. Actually, simple B&W laser printers have gotten really inexpensive. One other avenue to explore: CUPS (in Linux) may have a driver. My HP Laserjet 1012 wasn't compatible with Windows past XP, but it works great in Linux. Your VM idea might be something to pursue using Linux as another option. – fixer1234 – 2016-03-02T20:25:53.177