The black OEM Tesla center caps can be bought
here on TSportline, but they're $160 per set of 4. You can get black blanks on Amazon and eBay, but I can't vouch that they'd be a good match for the TSportline black color/finish.
My TSV wheels/caps aren't black, they're TSportline's "satin gray", which is apparently a match for 21" Uberturbines. I like the gray better on blue Teslas.
The TSV wheels come with TSportline center caps, but they have a silver logo that I really don't like. Sadly, there are no satin gray blank center caps (or Tesla logo ones) available anywhere, so I put in some work to make my own satin gray color-matched blank center caps. I made a set of color-matched OEM Tesla ones as well, but ended up going with the blanks because my MYP is de-badged and I think it works better.
Here's a post I made about the whole process.