Do the bumpers come off when installing a body kit and will they remain off or where can I find replacement rubber for the bumpers?

 

It depends... which body kit are you installing?

 

And if you decide to keep the bumpers and need new rubber guards, they can be had, but they're expensive. Even used, an "end guard" for a 280Z is probably $40 or $50, if the seller knows what they're doing (if they don't, score for you!). New, they're upwards of $125 each. All the usual supplier links for new and used usually have some inventory. If you go to a yard, figure under $10, but it's hard getting one that's not already torn up in the usual pick-n-pulls, at least around here.
Dave