Was wondering if anyone does this period and some thoughts on proxies. The Prussians and French are covered and I think I can use 1806 Prussians for Saxons and Italians maybe SYW for Russians? Now for Austrians I have no idea? 

I think we may be struggling with the Austrians.  The combination of headgear and shoulder-slung pack makes them very distinctive and tricky to match up with a reasonable alternative.

I've been reading a little about the Russian general Suvarov and his campaigns in the Alps. I think the Russian uniforms of the time were very similiar to the Prussian ones so this may be a better option for you.

Funny I actually saw a painting of Suvarov crossing the Alps with his army in Moscow art museum which is what got me thinking about the period. That and my love for the 1806 Prussian uniforms. 

If I follow up with the project I will likely do as you suggest and use Prussians for Russians. Its a pity nothing will work for Austrians. My guess is that a specific sculpt is not planed. I think other than standard Austrian infantry everything else is at least possible. 

If you do go ahead with your Project then could I recommend ' Eagles over the Alps' by Christopher Duffy;not easy to obtain but an excellent account  

I was looking and doing it myself but have lots of Peninsular War figures to paint yet.

You could do most with baccus. 1806 Prussians aren't really suitable for the revolutionary period.  They wore a different hat prior to leaving the war in 1795.  However, there are heaps of potential conversions here at baccus for other troops.

Check TMP for conversion advice on revolutionary war.