High Keep: #13 on map, the erudite Enchanter vendor, will sell to anyone. The banker and surrounding guards are around level 30-35, and if you can tank them for a bit there is no need for FD/sneak/wall shenanigans.
https://wiki.project1999.com/Classic_Merchant_Guide
I think this guide on the wiki is an attempt at doing what you're asking, but as you can see it fails a bit hehe. Could be updated for sure tho!