I think if you feel that you can handle a 3rd dog go for it! I would suggest that you start now by becoming acquainted with all of the rescues in your area. Fill out an app, get approved by several of them and develop a relationship with them.
Don't limit yourself to just GR rescue groups. Look on pet finder ect for local groups too. I know in my area there are several small rescue groups that take in all breeds of dogs but they're not well known, work on a shoe string budget but do great work. I found my Lady (GR) from a basset hound rescue because I had developed a relationship with them a year earlier so they called me when they found Lady.
That's how I've always rescued. Explain to them exactly what you're looking for and your time frame. Most rescues are fostered in homes and they get to know everything about these dogs, in fact they fall in love with them too.
I've done this with several of my past dogs, I've also had dogs come to me in mysterious ways. I believe our dog finds us if we make our-self available.
Just as the breeders on this forum know which puppy should go to which family, the fosters are great at this too and they always want to find the
perfect family for every dog.
If this is what you want to do I think it's wonderful for all involved! Be patient, sometimes it can take quite awhile to happen but it will happen. Good luck whatever you decide. (personally I'm hoping you do
EDIT: not sure if I made sense but sometimes a GR slips through the cracks and ends up with a different rescue group.