I got all my dimple dies from Cleaveland Aircraft Tool
in their RV tool kit. I'll break it down to required and optional.
3/32" standard die set
1/8" standard die set
#6 screw die set
#8 screw die set
3/32" close quarters die set (HIGHLY recommended! There are some tight areas where this is very useful)
3/32" modified male dimple (for tight areas)
3/32" small diameter female die (similar to modified male die for tight areas like flanges)
3/32" substructure dimple die set (dimples 0.011" deeper than the standard die for better fit of skin dimples in the ribs, spars, etc.)
3/32" fuel tank dimple die set (dimples 0.007" deeper than the standard die on the fuel tank skins to allow for wet install of fasteners with sealant without need for rivet shaving)
Tight fit dimpling fixture (I haven't used mine yet so maybe not worth it)
All of these dies are spring back dies and I can attest to the high quality of dimples these produce. I also use the DRDT-2 press dimpler and I get no distortion around the dimples. Make sure you follow the setup instructions properly and you'll be very happy with your dimples.