Where can I find a base for this lampshade? (Canada)

A Facebook marketplace seller is selling the shade for a lamp like this for $100 (last photo is the seller's). But there's no base. I asked the seller and she said she doesn't know how to attach the shade to a lamp and that she just found the shade and is selling it. I did a Google reverse image search and found that the bases for these types of lamps are particular so you can't put the shade on any general lamp. It appears to be some sort of Art Nouveau slag glass lamp? At least according to the titles that online sellers give the lamps. I don't know for sure. And I haven't found anyone who sells the base alone. The complete lamps all sell for $500 to $5000. Do I just have to bite the bullet and buy the whole lamp with shade from someone else? It would be great if I could find the base alone and save some money. It also looks like the lamp requires a sort of cap on top to close it (like in first image), so I guess I'd have to find that too? Maybe I am better off just buying the complete lamp from someone else