Head-Quarters will sell the heads outright, but better is the "core exchange" route--buy the heads with '"core charge" and get the core charge refunded when you send them your take-offs. No down time/no take-offs to sell.
Head-Quarters charges 450.00 core charge you can get a set of heads off ebay for 175.00
then sell your when your heads are done
Not sure what the point is since the core charge is refunded. Also, the core exchange route avoids issues with buying someone else's heads (are they as described or not, damaged in shipping, repacking them and shipping to Head-Quarters since take-offs will later be sold/shipped) and reselling your take-offs (listing for sale, answering questions, packing and shipping heads a second time, etc.).
If you use your charge card to get the work done and you haven't gotten the heads sent back in time just don't pay the $450 when the bill comes in. It takes less than a month to do this whole process if you don't dilly dally.