Try the American Rhododendron Site. They have pictures of many varieties. Yellow Rhododendrons R. wardii is the classic yellow. It is used in most breeding programs to develop new yellows. It is greenish yellow. But as you can see from the size of the list, there are many others. Here is a link that might be useful: ARS: Yellow Rhododendrons

How much shade was this plant in previously? Full-on sun is not a very good location for most rhodies in a zone 6 climate, especially with what appears to be a large boulder behind that may be reflecting heat. While PJM is considered to be a more sun tolerant variety, I believe the recent move to a more exposed location is causing stress. I would like to tell you the plant will eventually acclimate to the new location but I just don't have that experience for your area. All you can do now - with the exception of moving it again, which I'm really not sure I advocate either - is to make sure it gets enough water during the heat of the summer. And you could consider rigging up some sort of temporary shade structure during the hottest part of the day.

Protect them from direct sun, wind and deer. They will be OK. The sooner you plant them the better. Don't water too much. Keeping the soil too wet is one thing that will definitely kill them. Wilt-Pruf is only necessary if you can't protect them from the wind and sun. Wilt-Pruf is more important after planting since if you plant properly by opening up the roots, you will disturb the roots and cause some water stress. Here is a link that might be useful: How to grow rhododendrons and azaleas.

Perhaps your nearby plant shop meant that PJM had the smallest leaves of any rhododendron easily available. There are many rhododendrons, species and hybrids, which have much smaller leaves than PJM but none of them are easy to find and none would be easy to grow in areas with high summer heat/humidity. Many of them are not terribly hardy, either. Among the ones I have grown myself are: campylogynum v. myrtilloides, leucaspis, hippophaeoides, russatum, Maricee (which may be the species segeantianum), intricatum (which is very difficult to distinguish from impeditum), Blue Ridge (in my experience the hardiest of the "blue" hybrids). There is a large number of small leaved hybrids, mostly with purple flowers that have been developed over the years often with r. Impeditum as one of the parents. Bloom River Gardens has a good selection of small leaved species, as does the RSBG. Using any of these small leaved lepidotes for bonsai could potentially solve the hardiness problem, but wouldn't help much with the heat and humidity issue.