Your local LFS should be able to order you captive-bred ponies if they don't have them in stock already - many are now carrying
Hippocampus reidi from ORA.
However, if your limited to a 10g hex I would stay with dwarf species, which you will probably need to get via Ocean Rider.
Either way I would plan on the tank having no other fish than seahorses. If your going with a bigger species you can use liverock, but the dwarfs may get stung my inverts on liverock, so I would avoid it in a dwarf tank.
Plan on hand-feeding the fish twice a day (probably frozen mysids, or enriched baby brine shrimp for dwarfs).
I'm guessing you lost the fish last time due to an ammonia or nitrite spike, but thats just a guess. Small tanks are incredibly hard to keep balanced compared to larger tanks.
www.seahorse.org has some awesome info.
I'm currently considering setting up a tank for
H. reidi - my wife fell in love with them at a local LFS. I'm thinking about a 20XH or 30XH tank (might end up with a 45xh though) - vertical space is very important with ponies - and a fair amount of liverock (a little less than 1 pound per gallon I think) combined with a HOB skimmer (may just use a modified seaclown or prizm) along with a DIY refugium. A very thin layer of coral sand (less than half and inch) will go on the bottom.
I'll probably cycle mine with the liverock, and add a pair of ponies maybe 3-6 months later.
HTH,
Red