[rayjay]

I don't like the mixes either, and, if you try to cultivate them in any meaningful numbers, usually one type ends up surviving and the others end up dying off.
I prefer to start an amphipod culture by removing some at night from a reef tank (using a red light source) but if you don't have a reef tank, you could find someone local with a tank and pay them to harvest some for your starter culture. The LOVE live rock RUBBLE, and with some chaeto in the culture vessel as well, it affords the best conditions for amphipod growth. The chaeto makes it easy to just pull some and swish it in the display tank to distribute some of the trapped amphipods into the D.
The other way you can do it is to buy the Royal Reef package and physically remove the amphipods to use for your starter and then add the remaining pods to the seahorse tank.