I don't think anyone is going to go out of their way to make addons or missions pre-res compatible anymore, like it or not. But like El Fisho said, there are TONS of missions in the missions depot that do not require resistance. Your best bet is to sort by date, and look at ones that are a couple years old. It *should* tell you what version of OFP you need for each mission, but that part is often ignored by people who submit the mission. There are definately a TON of missions already out there for v1.46.
Speaking of which, you can patch your OFP up to v1.46 (instead of v1.3) off of flashpoint1985.com, or another OFP site. No need to stick with a lower version than you have to.
Now, if you REALLY want to play a specific mission or addon, there is a chance that it can be played in v1.46 with a few minor modifications. For example, when I had v1.46, I played a "resistance only" mission. All I had to do was delete two guys that had pistols. But I'd suggest you just play some of the hundreds of pre-res missions, until you can get resistance. To get you started, you can play mine:
http://www.ofpec.com/missions_depot/index.php?ID=586