On a recent visit to Oman and Bahrain I managed to get hold of many lots of stamps from these two countries.
 For Oman things are a little difficult, the post office prints low amounts of stamps and gives priority to philatelic club members then releases the rest for public consumption. By about 3 months the whole issue amount has been sold and the stamps can only be bought from dealers or swapped with collectors.
I managed to get almost all the Oman collection through a dealer in Oman but I had to pay a lot of money, mostly catalogue value or maybe even more, if anyone would like to buy lots of Omani stamps, use the contact form.
Bahrain's stamps are a little more easily found, the post office provides stamps from the last 10 or so years with FDCs, mini sheets etc. Bahraini stamps are actually really nice and a lot of effort has gone into producing them, I got hold of a big lot of Bahraini stamps, if you are interested then let me know by using the contact form.
Collecting from these two countries is an expensive hobby, their currencies are strong and the amount of stamps they produce makes them harder to get therefore inflating their price. There is also not much web presence for the post office of these countries and you certainly can't join the philatelic club or buy stamps online, you really need to be there physically or risk sending money over the post.