I have taken him to "therapy" playgroups where there is a therapist conducting relationships with children and therapy assistants helping get the kids together and that has done a world of good. They work together fostering relationships based on Stanley Greenspan's theories and formats of Floortime. It is a natural way to get kids to come into each other's worlds. If you contact Rosemary White in Shoreline, WA she could probably put you in touch with someone that does that in your area. She is one of my team members and a trusted soul.
Also, I've made playdates with any kid autistic or not that my son has shown any interest in. One kid we met at an autism group play session that was more geared towards providing something fun for the kids and allowing the parents to run away for two hours. I came back and my son was playing with another little boy (for the first time ever!). Both me and the other Mom were stunned. So, we set up play dates. The other Mom had an wonderful therapy assistant that planned and executed the playdates for the boys. She was creative and really set up crafts where they had to help each other to finish them or games where they had to play together to make it work. She was amazing. Unfortunatly, she had to move on and the playdates we have tried to do we weren't as successful with the boys working together and they had somehow lost interest in each other without her there to anchor them.
The typical kids we've had playdates with have been compassionate and we've known them for a while before having a playdate with them. I tried setting up playdates with typical and autistic kids this summer. I planned activities and then invited everyone stating that my goal was to involve the autistic kids in our plan. People came, but it was a bit like herding cats. I think it is better one on one or a very small group of just a couple other kids autistic or not.
I keep trying as I am hoping for my boy to make a friend his age someday. Good luck!

Initially, I always thought it would be best to have my ASD kid with NT kids, so he doesn't pick up any bad habits, etc.

However, as strange as it may sound, I find the ASD kids much better behaved and their parents much more understanding. I find ASD kids kinder, more understanding, and less prone to spouting insults (mostly unintentional) such as "why is your kid so weird?"

A few months ago, my son was playing with some NT kids and a child with some fairly severe delays. When my son hurt himself, the child with the fairly severe delays asked him if he was okay. The NT kids didn't say anything. My wife and I debated what response would be a normal response. However, we both decided that defining what the "normal" response was not the "best" response.

I wish I could not many kids around me on the spectrum and the kids in his class I have not got close to their parents yet.

FAMILY ADVOCACY AND COMMUNITY TRAINING - Mandy Shale, if you have DSPD Services there are Respite workers available in our area, we are currently attending Cta, there is a one on one adult assigned to your child, but they are in a group, the adults take them out into the community and they do activities together. This works well with my son because he seeks out adult attention and sometimes doesn’t want to be bothered with his peers. Other times he chooses to engage. It is kind of like having a big brother/sister, except they are trained on working with children/adults on the spectrum. Also there are other groups such as Rise were the kids are a little higher functioning and spend more time in the community. Both also have summer programs. They go hiking, swimming, bowing etc. Activities can be target to meet your childs needs. You may want to contact Mandy Shale http://utahgap.org/utahadvocacy/?page_id=8. Hopefully you already have DSPD Services, if not still call Mandy. Utah has a waiting list but it is a lifelong, invaluable service, In my opinion worth waiting for.

I have a friend that I went to school with, her son and mine are 1/2 year differance in age, but get together. I find it very helpfull to one another cause they have a friend they can relate too.