Phastek has bushings in stock now. I don't think they are made by the same person, but they look very similar. I have a set from them. I also have a set made by Thapilot that have o-ring grooves machined into them. I think he may have sold all he made already, though (check his add in the for sale section). I think either would work just fine, but the ones with o-rings would be quieter.
2011 2SS/RS LS3/M6 RJT, GFX, ECS Blower, FSP Blower Cam, SW 2" headers/3" exhaust, 3.91, built by Florida Speed and Power 745 rwhp, 620 rwtq
2012 Silverado 3500HD SRW Duramax/Allison