Jack-
I have a RV-12 that began construction in 2012 ... at that time the large box of 10K rivets had a label stating the manufacturer was Gesipa and at that time the part number on the box for the rivets Van's calls LP4-3 was Gesipa PolyGrip MultiGrip GSMD41-43APG. Gesipa rated those rivets as having Grip range = .039" - .197" Shear =162 lbs. Tensile = 236 lbs.
In 2016 Gesipa changed the rivet name to just PolyGrip and their specs are now in mm. Also, the part numbers have changed to all numbers and the grip range has also changed slightly. Looks like the 143 3822 is the new part number for the LP4-3. From the Gesipa 2020 catalogue, the new part numbers for the PolyGrip aluminum/steel shank rivets are:
143 3822 for 3.2mm (1/8") x 8mm Grip range= 0.5 - 5.0mm
143 3823 for 3.2mm (1/8") x 9.5mm Grip range= 1.5mm - 6.5mm
143 3824 for 3.2mm (1/8") x 11mm Grip range= 3.0mm - 8.0mm
You may get lucky and find a local source for Gesipa. When I started my project, I called Gesipa and was given a contact for a local distributor .... at the time they would not sell retail (even though I wanted to purchase 10K) ... only through distributors, I assume it is still that way.
Hope that helps.