Any 'bolt on' aftermarket accessories, like seats, grips, bars, pegs, mirrors, exhaust, and light, listed for the Intruder 800 or S50 will fit your 750. No one makes an aftermarket rear wheel, because the shaft drive and drum brake make the rear wheel unique to the Intruder. As for engine parts, no one makes aftermarket performance parts for it at all (no cams, valves, heads, pistons- nothing), so your only choice is to rebuild the motor using dead stock parts. And for this you have to get parts from Suzuki. Most folks find that an engine rebuild is just not worth it on these bikes, as the price of the rebuild is far higher than the book value of the bike. But if you do all the labor yourself it is probably worth it. EBC and Barnett can hook you up with things like clutch parts and brakes.
Why does it need a rebuild? If it is smoking and needs rings, or the gaskets are dried out and leaking, that is one thing. But if the motor tossed a rod and is blown, then the internal clearances are so tight that the engine cases are usually damaged and a new motor is called for.
As for turning it into a 'head turner', check out the member photo galleries at 'intruderalert.com' for some ideas. Some folks have bobbed theirs, others have chopped theirs, so there is a wide range of styles.