i use http://www.johnsonstelemetry.com/
for their collars and i use a wildlife box
http://www.wildlifematerials.com/
I use these on bear hounds and iam not sure of what type of application your looking but these work exceptionally well for me.
there are others that you may find easily on most search engines, magnum telemetry, quicktrack,and, wick outdoor works carries a line of tracking collars as well.Hope that helps you out!