I have a climber rated for 400 lbs that I got from 'Big Man Treestands'. I don't know if they are still in business but if they are they can fix you up. Also, the Summit Goliath is 350 lbs rating and a little borderline for you, but it came with a Seat-O-the-Pants with the same rating which I still use.

I am pushing 300 lbs myself so I know you got to find something that suites you. Hang in there, you will find it. I don't eat heavy either for the most part. My heavy weight is largely cause by thyroid issues. Good Hunting!