Creating a schedule of games with "Conference" and a randomized "Non-Conference" with varied conference sizes

There would be 30 total games where 12 are non conf. and 18 conf. The conference are no smaller than 8 and no larger than 16 and can have odd or even numbers. There will be up to a couple hundred schools to matchup. If there is an odd number there will be non-conf games mixed into the conference schedule. I am thinking of making it 31 or 32 weeks and adding a bye or 2 byes so that will not have to happen.

I am using swift.

I have tried creating randomizing all possible matchups and then creating the schedule from there and having troubles. I also have done the basic round-robin equation but it doesn't work for odd number without a bye.