Just about any full-frame motorcycle needs the motor pulled to do any major engine work, so the Intruder is no worse than any other bike in that respect. Parts for your 750 are readily available, but only from the dealer. Some are listed as discontinued, but they have all been superseeded with a part from the 800 motor that is the same except for the part number. Aftermarket companies don't make parts for it because it was only in production for four years, so there is a very limited demand. In addition, most people just toss out an older metric bike when the motor blows, or they swap in a used motor, so there is even less of a market for new engine parts. I mean lets face it, a 17 year old Japanese motorcycle isn't worth putting $2000-3000 worth of engine work into, as you could buy another used Intruder for that. I picked up a 1993 Intruder 800 with 7000 original miles for less than $2500 bucks back in October.
Finding someone to swap a motor is easy, but no one wants to pull your motor apart bacause a rod knock usually means the crankcase and probably the crankshaft are damaged, so they don't want to spend a lot of time on something that can't be fixed anyway. Shops get burned all the time on thsi: when they tell an owner, "sorry, can't be fixed, that will be $500", what do you think their chances of getting paid are? I bought a used, low miles 800 motor out of a wreck for $400 last week, a better choice than trying to tear down and rebuild the old one at $50 an hour plus parts. I have seen running 750 and 800cc Intruder motors on EBAY go for as little as $250.
Old intruders are great bikes for the money. My 1993 now has 22,000 trouble-free miles on it and is just now getting broken in, and my 1996 Intruder 800 went 132,000 before the motor finally went. I know several folks with well over 100,000 on thier Intruders. Intruders are known for being bulletproof, so if your's tossed a rod at only 24,000 miles, I'm guessing the previous owner was not real good about changing the oil, or the bike was run out of oil at some point and the bearings were trashed.