For mc18 bodywork now you're looking at 2nd hand or dodgy chinese ebay pattern panels.

To say an RS250 fairing "fits" is a bit of an overstatement.

The NSR250 mc18 and RS250 nf5 are pretty much the same bike, the differences are the seat subframe is different, so the seat unit will need modifying to fit.
The bodywork mounts are different, so they'll need moving or redrilling
The screenbrace is different, so that'll need sorting and the bars will be both to high and foul the fairing before it gets to full lock.

But when it's all done it'll look a bit like this (ignore the seat), or if you use a later fairing you could do one that looks like this, that's an mc28 bit you get the idea.
Basically the RS is the same size but not much else.
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