If you want a yellow tang then the only source is captive bred or from an existing hobbyist. I'm a fan of Biota so would recommend them and buy direct. Understand up front that they will come in on the small side. Biota does sometimes offer larger yellows for an additional charge. Up to you which one you prefer but having bought several fish from them over the years I can say the smaller size hasn't impacted me at all. If they are too small I simply place them in my refugium for a month and then into the display. Works amazingly well.
You can search on Biota yellow tang and get hobbyists comments but the general theme I've read around the internet is:
1. size, small
2. color is somewhat pale
3. grow quickly and color is perfectly fine - it is a grow, maturing thing
Captive bred fish is the right choice and the only way we can legally obtain yellow tangs today. Biota has been working on their production of them for a while now and aggressively provided high quality fish once the ban went into effect. While I do not personally own a Biota Yellow (I own a scopas at the moment and not sure he/she would welcome another Zebramosa Tang) I do own Gold lined rabbit, sapphire, forktale blenny, radial filefish, matted filefish, and a starry goby in my 210 display. I have 4 of the pink square anthias due in next week along with a goby which i forget which one darn it. My point is that I've had 100% success rate when buying direct.
Ok, so you know I own Biota fish, a tee shirt, and obviously a fan of the company and role they play. Now the fun part. Be prepared for the size and lack of color at the start. Have some food ready preferably what Biota is feeding if you can get it. Also nori. Not sure the size of your display or other fish but if you have other tangs that are larger or Zebramosa's then this may not be the right choice unless you have an isolated tank/display to let it grow and decoys / mirrors so not to draw attention. If it is the only tang then you are set. Larger tangs vs captive bred new isn't going to work in my opinion.
Not sure if this helps but Biota's yellow info below. Also email them and they will get back to you about your questions.