Just about every custom supplier I've seen makes 2x, and quite a few have 3x. Not sure who our screenprinter is, but the jersey blanks for my company team are from Voler. We had a few 3x on the team.
Race-fit 3x is going to be different than club-fit (shorter sleeves, tighter cut, etc.) but should still fit if 3x is your usual size. The only one I've found to run really really small is Woolistic. I can usually slide by with a 2x in a club-fit, if the length is cut long. In Woolistic jerseys I need a 3x, and I have to stretch 'em a little bit to get the length on it
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"I feel like my world was classier before I found cyclocross."
- Mandi M.