Does anyone know where I can find another card like this, or where I can buy this card?

Presumably you're talking about one of those motherboards where it has, e.g, 5 USB ports, but only two of them are on the ATX panel, and the others are just headers on the motherboard?

My Asus board came with this kind of thing, but it included the relevant thingummy that you screw into a spare gap at the back (i.e. into the hole in the case, not actually into a slot on the board). It's effectively just a piece of metal with some ribbon cable attached to it.

So, assuming that this is what we're talking about, what kind of motherboard is it? Do they sell spare ones?

Alternatively, as andy says, USB 2.0 cards are relatively cheap, so you could just give up on the internal ones.