You could try the salvage yards like Wentworth for an engine.
However, O-200's are getting very hard to find and command a steep price. Ordering an engine from Continental used to be a viable option, but they are not currently accepting orders (as far as I know) because of the lack of crankshaft availability.
A field overhaul or an overhaul at an engine rebuilding shop is also a possibility. But, (and it's a BIG but) your crankshaft better be reusable or you're in for a LONG wait. And, as you noted, your plane will be down for 16 to 24 weeks while you wait for your engine to come back from the rebuilder. It could be a little less if your local mechanic does a field overhaul.
I won't bore you with the different types of overhauls since I'm not really up to speed on "Factory overhaul", "Factory reman", etc.
Good Luck! I hope that you can find an engine that will be rebuildable so you can minimize your downtime.
