Lucky bags? They're common for artists to clear out old stock! I do them myself, they sell well at cons
I wouldn't call it gacha though, there's negative connotations + some conventions get real iffy about even insinuating gambling
imo i'd just label the last as custom commissions, connotating it as gacha makes it seems like the buyer won't get what they want or get something random... generally the idea of lucky bags are to sell your merch at a lower price to clear stuff out, so I wouldn't set prices too high
ETA: here's mine for stickers and buttons for ideas! I like to give a loose idea of what's in there (IE fandom/original) and package them pretty, it draws more people in