it will be extremely hard to find a mouse without ANY plastic on it at all.
the steelseries wow mouse a few other mice have quite a bit of metal on them however do have some plastic parts. this is common on most gaming and casual mice.
the mouser mouse is wood and metal with rubber wheel
if plastic is your issue then what about rubberized coatings on mice? the sensei raw, mionix castor and various other mice are mostly covered with a coating. the side buttons may be plastic still though.
as mentioned earlier, you can find various wooden mice on the market as well. they may be a bit heavy or odd to use with fast paced movement though but i havent used them so have no idea how well they handle.
if you have trouble with plastic... how do you find a keyboard fine? most are plastic. various other containers, the pc case and other life items are plastic as well.
i'm thinking you may have some other condition unless you have noticed such reactions throughout your entire life.