Sea Legs tablets seem to be still available online and a 'news' search on Google doesn't produce anything to suggest that they've been withdrawn.
So it's either just a temporary supply problem with the manufacturer or, probably more likely, pharmacists have decided that they can make a bigger profit margin by selling the same product with a different brand name on it.
Ask the pharmacist for 'meclizine hydrochloride' (or simply 'meclizine'). He'll almost certainly be able to provide you with some tablets, which will be exactly the same as Sea Legs, just in a different box.
Incidentally, if you like crystallised ginger, it's a wonderful preventative for travel sickness!
Chris