And just last night on my level 20 alt who is just leveling diplomacy I got three grade 2 rich medical supplies missions in five runs (and I just got him to grade 3 last night).
Out of interest, is your character imperial or a member of the republic? I've noticed that a lot (possibly all, though I haven't done exhaustive checks) of the rich missions are split between imp/rep variants, so it's possible that a republic character sees different results.
My point is, IMO, trying to get the mission you want by changing areas is a waste of time. If you do not get the exact mission you want, then go for the next best thing (depends on what you consider next best), let that mission run and try again. This has also worked for me VERY well with grade 6 UT metals missions on my main, and my scavenger alt when I need Thermopalst Flux.
That's what I usually do too. Generally I don't even mind running the gift missions, especially rich ones, since they sell quite well (and can be used to boost affection too). Eventually I settled for the abundant medical supplies mission once I had established that I wasn't going to get a rich one.