First off, I wouldn't suggest two - a trio (1 male, 2 females) is better or else go for just one male. Unless, of course, you can buy an adult pair that have been together a fair while.
One of the problems with buying online is actually precisely that you can't be certain of the sex or, indeed, health. I have had mixed results when buying online but. to be honest, honeys should not be forcing you down this route anyway. They are a very common fish - you can probably ask your LFS to order some in or ask again about them as they may have just run out when you last visited.
Just bare in mind, also, that they are probably not a good option to start your tank off with. Even if you have fishless cycled, it's best to put the hardiest fish in first.
In answer to your actual question
- you can take a look here:
aquabid.com - depends on the seller how likely things are to go well and shipment may be a problem depending on where you live
http/www.aquarist-classifieds.co.uk/ - limited but definitely worth a look if you're in the UK
http/www.dartfordaquatics.co.uk/ - have not tried them myself but know of someone who has with good results
http/www.aquariumfish.net/pages/price_list.htm - never tried them (and I'm a little sceptical)
There's also always ebay (e.g.
http/stores.ebay.com/zoostock ). To an extent, it also depends on where in the world you want the fish shipped - not everyone can do everywhere!