I have a 1990 IWG 400 and im wondering what front brake disc, rotors, will fit the 1WG from other bikes ? anybody know.

Which 1WG ... that's the question

If you have air intakes above the headlights it's a 1988 3EN1 - which have 285mm Dia discs
TZR 250 3MA and 3XV (jap imports)

Air intakes below the lights and it's a 1989 3EN2 - which are 298mm
FZR400RR 3TJ, TRX850, FJ1200, TDM850, FZ750, FZR600, FZR600R, 600 Fazer

Measured my front disc, they are 280mm, i know its a 1wg 90 USA model, so i know in the UK there are like 6 million versions of the FZR400, so im still trying to figure what other disc will work.

This is how my bike looked when i got it, so now you can see what model it is.

http://i720.photobucket.com/albums/ww20 ... AG0181.jpg

Your bike is a FZR400 Genesis model, and quite tidy by the looks of it.

The link is for the EBC brakes page, if you find your model (page 52) you can copy the code MD2020 and do a seach, you'll find on page 402 they list the disc first and the bikes it fits after and yours seems to be unique.

http://www.ebcbrakes.com/Assets/2010-UK ... alogue.pdf

As yours is a nice you might consider EBC discs as a replacement. I think the caliper you have are ... 85mm ish bolt spacing in which case you could probably fit 3TJ calipers.
The alternative would be to get the front end from a FZR600 and fit that to your bike.

Thanks for you help, and for the link.

You might try the 3en1 disc - they're the same size but I'm not sure about the offset.