I've gotten quite satisfactory xxxxl bib shorts on eBay, Polish manufactured (insert obvious jokes here) sold by GearLink in Florida.

For shirts, I've found that even the big sizes are designed for an NFL outside linebacker, not an "American cut" body, and so I find that fan-replica sports jerseys are made out of the same material that helps with drawing the perspiration off, and are bright colors the drivers see.

For cool weather, I wear and recommend soccer goalkeeper's jerseys, as they're longsleeve and thicker (for warmth) and even have padded elbows (for those low speed tumbles when you're learning how to get out of clipless pedals!!)