Your best bet is to trade for a Tepig and level it up into an Emboar. The easiest way to do this is to breed an Oshawott by putting your Oshawott or its evolution into the Day Care with a Ditto. Ride your bike around the area for a little bit, and soon the Day-Care man will call you over and give yo a Pokemon Egg. Once this Egg hatches, you'll get an Oshawott.
The next is to go the the GTS at the rightmost person at the second floor of a PC (assuming you are playing B/W, B2/W2). Go to Global Trade-GTS and put your Oshawott up for trade for a Level 9 and Under Tepig, which means you will most likely get a baby (level 1) one. Wait until someone accepts your trade, and you'll get your tepig. Level this tepig up to an Emboar, and you'll have the full evolution line in your Pokedex.
Hope I helped! Sorry if this looked complicated.