It would help to know how old she is. If she's young and doesn't really know what she's wearing, then you send her in clothes you don't care about. She either comes home in the same ones, or she comes home in something else he put her in. Next visit, she wears those same clothes back to his house, and you're only out two outfits (one she leaves there, one she's wearing).
If she's older, she can take responsibility for packing some of her things, but if they don't come back, you don't keep providing new things. I would email or text him a list of what's packed and what hasn't come back and which therefore is in his apartment/house somewhere (shirts, pants, socks, underpants, sweaters). Make it business-like and matter-of-fact, no judgments or accusations. Say that, since so many outfits are at his place, you are making it easier by not sending any more clothes. Then you will have documentation if anything comes up later on with a lawyer or judge. Keep a running list, and if he says he doesn't have anything, then you can email him a list of 30-40 things that haven't come back. I wouldn't make a big deal of things like single socks or mittens - we all lose those in our own homes. But lots of outfits? That's another thing entirely.
Do not send her with anything important! If he has some special event going on with her, then he can manage that. I gather he is not paying a lot of child support (which you imply he is not because you say you spend your own "hard earned money" on clothes) but be careful that you don't take child support and then say you aren't spending it on her. But you can certainly limit what a child takes on a weekend.
It's up to him to buy more or run a load of wash, period. Stop enabling him. Just don't get sucked in by any manipulation by him - you have to stay calm and not get sucked into his motivation and saying he's got a problem with you. Maybe he does, maybe he doesn't, but getting all riled up doesn't help your case at all and it does get him all puffed up with himself if he is trying to get under your skin. The trick is to not let it get under your skin! Your attitude has to be, "Dad's house, Dad's rules, Dad's in charge" - and that means, if he chooses to dress her in ripped sweatpants, then so be it. No child ever died from wearing the same clothes 2 days in a row. She has to work it out with him without you being involved. If you don't get sucked into the drama, he will have to deal with her or she will have to keep track of her stuff (if she's old enough). Your comment should be, "How unfortunate for you" (that he can't find things, that she doesn't have her favorite pink shirt, whatever). No emotion, just facts. Don't explain, don't nag, don't beg, don't get resentful and go buy new clothes, just let it go. He'll either be responsible (if he's irresponsible) or he'll calm down (if he's doing this to get a rise out of you).
This is not your problem to solve - so don't try to.