I second the part about checking at Petsmart...the only
lfs I have seen them in is one Petsmart near me, but they only get a few and tend to last just a few days and then they are gone. If you have a Petsmart and can get friendly with the fish manager, they might be able to special order some for you if they don't currently have any in stock.
whitetiger gave a lot of good ideas; I have actually seen some all-yellow guppies (well really white fading into yellow) that are quite amazing. And one of the most obvious fish of all is the Lemon Tetra, though many
lfs' don't carry those because they tend not to ship well.
Do you by chance have an aquarium/tropical fish society anywhere near you? If so, definitely make contact there...I am sure you could get a lot of these fish from other members, pay far far less than store prices, and the fish are likely to be 500% healthier than fish you find in
lfs' as well.
The other option for the Golden Wonders or other killies is to order the eggs by mail (listings through the AKA are usually around $8 plus shipping costs). Now granted, you need to be able to have a set-up to hatch out the eggs and keep the fry alive until they can grow some...(i.e. a few small containers, the ability to grow your own "fry food" like baby brine shrimp or microworms, etc.)...but if you can do that successfully, you might end up with upwards of 50 (or more) Golden Wonders for around $15, or the price you would pay for 2 or 3 of them if you buy them at Petsmart.