Hi there! I try to keep up my shelter surgeries amongst the volunteer (and one PT vet) each week. We also partner with a mobile low cost spay clinic that comes to the shelter each month. We also use our local vet clinics to help us with spay/neuter as well. Obviously during the peak season, it feels like I'm barely keeping up :)
What I've found to be most effective is:
1. Have a contact person at each clinic so the information is stream lined. By talking to one person, they can coordinate with the surgical schedule and let me know what they have time for. Each doctor seems to have a preference of what they will do (size of dog, age of animal, preference kittens vs cats, etc.)
2. Having volunteers transport to clinics. It saves a lot of staff time if we can have volunteers or fosters drop off and pick up. I send all the relevant paperwork ahead of time
3. Scheduling animals that will do the best in a clinic setting (i.e NOT super shy, dog aggressive, feral) It makes for a smoother experience all the way around
4. Bribe! I stress bake like a boss and the local clinics can often be "bribed" with home made baked goods at tweaking schedules. I usually use this for when I need an x-ray or a drop off day admit appointment.
5. Understand that most clinics absolutely want to help where they can but cannot fill their entire surgery schedule with discounted spays/neuters. Sometimes I've been able to ask if they could do a "cat neuter-a-thon" or could they fix a litter of kittens plus mom. That seems to be something they can work with and look at the schedule if that is my need.