I'd like to know where; cheapest I've found is $35 on eBay. :unsureHonestly, you can pick them up for less than a can of orange paint.
"All i need to do now is make the red end cap to make it screen accurate "
Try going to a bike/ car repair centre and ask if they have any new oil cooler fitting covers, these are usually red push fit caps they cover the openings on new coolers to protect them during manufacture and they leave them on till end use, might be just what youre looking for.
see attached pic of these covers on a cooler they look about the right size too..