You're not accounting for public databases of open source items. We've seen glimpses of what its like within starfleet for starfleet tech/gear and a few little bits of what its like for starfleet personnel who want to replicate non-starfleet items(like the Klingon candles Dax made).
Just look at websites like thingiverse for 3d printing today. A thriving community of open source designers...Add this to the non-monetary systems of the core federation worlds and I would posit that it would be a mainstream part of life to be able to access many multi-planetary databases of items, designer clothing included.
And please speak for yourself, I design most of the shirts I wear before having them made