Supposing Buckland already has a great stock of ponies of its own? Of course, that begs the question of why these particular ponies didn't already have names, but it would make a lot of sense for such a wealthy and powerful family to be in the breeding business.
Under these circumstances it wouldn't be such a big deal for Merry to make off with them at the last minute, and considering he himself is already disappearing the fact that he was running off with ponies wouldn't cause so much talk.
Plus if Buckland is into breeding, that might explain some of the affinity Merry has for Rohan, and my fic-minded self has already suggested that as a result Buckland has the best ponies in the Shire 120 years down the road...
On a side note, go to Mordor you spammer.
