I'm working on this costume for my 10-year-old to wear to Dragon Con, and I'm trying to do it by buying off-the-shelf pieces with only minor modification.
The shorts look like mountain-biking shorts. [I've removed the links I previously posted. The shorts are much darker in person than they appear online, so they don't work after all. I'm going to explore modifying some regular cargo shorts.]
What is really bugging me is the jacket/jersey. I can find plenty of cycling jerseys that have those colors, but they are always inverted, with the neon/high visibility green as the dominant color and black as an accent color. Also, the collar is generally much smaller or even nonexistent. Track jackets tend to fit the color scheme and shape a bit closer, but since my little guy will be wearing this in Atlanta in the summer, anything the slightest bit insulating is completely out of the question. I'd love to hear if anyone else has found anything that fits the bill.