Ray,

A source? NO.
However, you don't have to be an expert dyer to get excellent results yourself. Just get a Lady Claroil hair dyeing kit, lots of different browns so pick the one you want, and follow directions. First wash the neck with some type of dish detergent and luke warm water. I use Dawn. Rinse thoroughly and pat dry. For a single neck don't use the whole kit. About 1/4 of dye and developer should be more than enouigh. The process is very simple, won't take more than an hour, you won't ruin the feathers and you'll get excellent results. Even I can do it! If you have a grizzly neck you might even try to do 1/2 and see how it comes out.
I strongly suggest that you NOT use a hot water bath dye.

Allan