I’d inquire at the various shave forums/groups you’re a part of first before trying eBay or a company that’s restored a razor.
A lot of spots have a BST. So if you have permissions for that, just post that you’re looking for one and find a nice trusted long time member to buy from. There’s lots of folks out there with large collections that can be convinced to part.
Companies that restore razors will usually be the most pricey. Spots like eBay are a crap shoot. First do your research so that you know to a reasonable extent what a red tip looks like compared to a super speed or something similar. Ask for pictures, confirm nothing in the mechanics is rusted up or loose, look for a 100% rated seller. If they dodge questions, don’t give you what you’re looking for, or aren’t open and communicative, don’t buy.