Lots of folks added the keys. Remember, too---when those jeeps were first sold off---most guys wanted them to be decked out like the CJ's which were on the market at the time---almost identical to the surplus jeeps but several times the cost. So as a consequence, most old GI jeeps still crawling the Earth today have gone through many 'costume' changes over the years. It is not unlike what happened to all those 'sporterized' Mausers and '03's (trying to keep this somehow weapons related...).
We have a 1952 M38a1 (owned by our family since 1955, the model that spawned the famous long-lived CJ-5). To my knowledge it has had no fewer than five different colors, has had key ignition, has had civilian tops, has had seat belts, commercial parts, etc.
My late Uncle, who owned it for four decades, spent years restoring it very closely to 'as issued' not long before he passed away some years back after decades of hard service. While we don't take it rock climbing, we treat it like a jeep and it does get dirty and go off road once in a while.
Long story short, there are still TONS of old miltary jeeps out there on ebay and such. My advice, go for one with as little rust as you can and a solid running drive train. Getting all the right do-dads and weapon mounts, etc is costly---but a RUNNING jeep is FUN right now and can always be 'prettied up' as you go along. It *is* fun to bop around town in something with no seatbelts and a no-key foot pedal start---but they *are* very dangerous if you don't drive them like jeeps--they will flip over and get you killed in a heartbeat.