If you are on Facebook, both Dallas North Aquarium and Fish Gallery have pages on there. DNA is really good about answering questions left on their page wall...so you can 'like' them and ask them about the black ruby barbs, they usually answer in like 2 days...of course calling is faster...but on FB you get their stock updates when they post, Fish Gallery too.
Bottom feeders for cichlids is a difficult task. There are two kinds of possible tankmates that are generally the most accepted, which is a pleco (not one of the small ones, so no bristlenose or clown), and some medium to large sized catfish that can defend itself if need be (not like a pleco isnt in the catfish family, but you know what I mean, lol). As far as fish being red listed, it usually is still possible to find them in stores, they just have a higher price tag... example boseman (spelled wrong, sorry) rainbow fish are on the list too, and you can get them for $11-16, even at Petsmart. If you want the black ruby barbs, call DNA or Fish Gallery and ask them if they can order them for you or if they have them how much. I have never seen black rubies in stock, but then again I only go maybe every month or two (when I need specific things or higher quality when getting a delicate fish).
Out of the barbs you mentioned, I would say the black ruby is a better choice than the tigers, especially if combining them with peaceful cories/bottomdwellers. Carndinal tetras are a good option, as they can handle a wider range of temps and arent as overbred like neons. However, my five neons have been doing great despite the fear I had that they would die since they were petsmart sale fish. I think green tiger barbs are beautiful, but they have personalities the same as regular tiger barbs. Have you looked into Odessa Barbs? I love them!! Or dwarf neon rainbows?
Fish Gallery on Greenville Ave in Dallas has the highest quality of fish, yet their stock isnt as desired on variety, but thats because they prefer to use only the best suppliers. Their fish prices are hit or miss as far as high or low...I've bought fish that cost twice as much at chain pet stores, and get it for half the price there...then again, others are twice the price you would pay. DNA is good, for the most part. I dont value their fish knowledge there though, I have often heard them giving misleading advice and telling people sizes a few inches smaller than they really are. And if its anywhere close to closing time, they rush you like no tomorrow, dont pay attention to what you are telling them you want and just irritating. However, they are closer, and they have a great variety of stock, decent quality of stock, and are fairly close to Irving.