You won’t find much choice with clear products other than regular varnish or danish oil because a lack of colouring pigments doesn’t provide adequate protection against ultra-violet radiation.
A light coloured stain is the nearest you’ll get to ‘clear’ and most brands are OK. Sikkens is one of the better choices if you don’t mind paying a premium. If you are certain you want a clear finish ‘OsmoUV Protection’ is a good bet.