IS THERE A SITE FOR SHARING AND READING LESSONS LEARNED FOR BETTER BUYING POWER?
Currently the Better Buying Power 2.0 site at http://bbp.dau.mil/ displays some best practices within its parameters, although not always specifically called best practices or lessons learned. DAU is in the process of creating an acquisition proven practices/lessons learned (AP2L2), which will be deployed to the public in early August at https://dap.dau.mil/apl, which will provide a consolidated site for locating proven practices, lessons learned, and award information for various topics. Currently for the BBP, it will have two areas, one for Performance Based Logistics and one for Should-cost (Should-cost a restricted site and will only be available to AT&L Government workforce, and will not be accessible until mid-late September).
As for other best practices and lessons learned, each DoD component collects and distributed into their own Lessons Learned systems. Many of those links have been identified at the https://acc.dau.mil/ppll site. If you have the permissions required by the system owners, you could also search those sites for information.