Can FAR 12.6 be used on its own, or must it always be combined with FAR Part 13 or 15?

See FAR 12.203 -- "Contracting officers shall use the policies unique to the acquisition of commercial items in this part in conjunction with the policies and procedures in Part 13, Simplified Acquisition Procedures; Part 14, Sealed Bidding; or Part 15, Contracting by Negotiation, as appropriate for the particular acquisition."

So you can take you pick, as appropriate -- 13, 14, or 15 -- which one best fits your needs?

Then, whichever you have decided, see FAR 12.603( c )( 2 )( ii ) for some of the items you need to include in your combined synopsis/solicitation -- "The solicitation number and a statement that the solicitation is issued as an invitation to bid (IFB), request for quotation (RFQ) or request for proposal (RFP)."

You cannot use FAR 12.6 "on its own."

Thanks! Interesting. I have seen GAO decisions that describe the facts as if the agency used FAR 12.6 "on its own." But they also describe the solicitation involved as an "RFQ." So by inference, the agency must have done the solicitation under FAR Part 13.