I figured out how to try on all the things on the wardrobe (so much fun omg) and made another avatar I'm pleased with, and I'm going through my wishlist to see what items I can buy with CSC to see if it's worth buying some, and a lot of the items do list "This item can be found in these locations: Cash Shop - Boutique" when you shop search it, but when I go to the cash shop boutique page that set isn't listed there. Is there another page I'm missing or did they retire but the shop search just doesn't reflect that?

Unfortunately the shop search only indicates that items have been in the cash shop. Retired items still show up. :c

Unfortunately, the shop search isn't programmed right now to say if it's not in the boutique currently. There are a lot of old Delish sets and the like that are semi-retired CS Boutique sets. Some of them may be brought back occasionally during different seasons for a limited time, but if they're not there currently then the only way to get them would be to find one to buy from another user.

Ah, okay that makes sense! Thanks for the help :)

No problem, good luck finding what you need! Or you could always add the items that aren't there now to your wishlist and see if they get brought back in the future (especially if there are none in shops).