First - you're right about the selection based on the model being new - it's always the case - the longer the bike is out, the longer the aftermarket has to catch up.
Differences between OEM and other? There's certainly pros and cons on both sides. With OEM, you going to get parts engineered specifically for the bike, which are guaranteed to fit and have the same quality as the original machine.
On the down side, backorders and shipping delays are a BIG problem right now. Also, the OEM rarely provides the same variety and selection of custom parts that the rest of the aftermarket can, Yamaha/Star has ONE optional exhaust for the Raider, the aftermarket has already provided more than ten (granted, some you wouldn't put on your lawnmower).
Regardless for how long the bike has been out, there are certain parts that the OEM will never come out with.
To add a little twist, keep in mind that many of the "OEM" accessories actually come from aftermarket companies, i.e. the Yamaha accessory windshields for the Raider are actually made by National Cycle.
Pros for the aftermarket - huge selection of option, again, some of which will never come from the OEM. Prices are almost always certainly better. Compare Yamaha's SpeedStar Drag Pipes at list price $797 to Cobra's Speedster Slashdowns at $590 list. There are many more sources for non-OEM, and the parts are almost always in stock somewhere.
On the downside, there is always a question of quality in the aftermarket. Any problems can be avoided by sticking with those companies that are reputable, and by participating in forums like ours where the opinions are as plentiful as the parts on the market.
Where to get your wish list (this list is not exclusive by any means)
1 - Performance Edge
2 - Cobra - two different sizes
3 - PE again, though certainly check Ebay.
4 - Morton's
