Great store one on one service if looking large quantity and various sizes local Philly master breeder Mr Gill Hart has hundreds of Angel fish at MPAC on Facebook My Philly aquarium club but please support local shops first!
I can't speak to the koi question specifically, but the people at William's Greenbank Aquarium are friendly and knowledgeable. It's a small shop, but is packed with all the stuff you can't get at the big chains like personal service and people who care about what they are doing.
Not sure if they carry them or not I went in looking at plants and stuff for bettas and they're snails they do have different stuff you need to go see in person to make a decision aquariums stores ain't the way they used to be
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