I happen to have a photo of the oil pan I use, taken when we had the (equally inane) discussion about "how much more oil you can drain out when you put the bike on the side stand".
By the way, this is how much... (not worth the effort)
I have no idea where I got that drain pan because it is almost as old as I am. Probably some department store.
It has the added advantage of three flat sides, so when it is time to drain the final drive you can push it up against the rear tire sidewall and catch all the lube oil. You
DO want to
drain the final drive with the bike on the side-stand if you don't want a well lubed rear tire. Then just put it back on the center stand for the re-fill.