On https://boltcard.org/ in the FAQ they list several vendors. You need NXP NTAG424 to program them as boltcards and pay contactless with Bitcoin (from your LNbits instance or BTCPay Server).
I got my cards from ZIPNFC, you can get just the tag on a sticker. But compare to simple NFC tag they are not cheap, close to 1$ each.
https://zipnfc.com/catalogsearch/result/?cat=&q=nxp+ntag424