There is this one which is sold by Amazon (not a third party) and is also sold in MicroCenter in Denver, but that is probably a bit far away for you.
You could also try this one advertised to support its sibling scanners by a third party. The reviews on this one is a bit suspicious with a few that says that it actually outputs 12V.
I would probably test all of these adapters with a multimeter first though to verify that it actually outputs 9V to the tip like it says it does.
Unfortunately, there are not really very many accessories of this kind available from a trusted source anymore.