You can buy rubber lubricant in an aerosol but I think it's mainly for things like seals on windows etc.

spray a 'little' dashboard cleaner or something with a bit of silicone in it on the pulley and see if it takes the squeal away.....it will only last a few minutes.

DO NOT USE OIL (like WD40)

If it does I'd change your belt OR loosen the tension a bit, I'd say your belt are old and have gone brittle.