The pre-1866 Austrian Infantry could be used for Mexican Infantry for both sides of the Maximillian Adventure. For 1866 the Austrians in Italy wore sun covers/Havelocks on their kepis and greatcoats with the skirts turned back. The Airfix/HaT French Foreign Legion can be pressed into service, though the kepi is a tad to short.

I picked up a number of boxes of the Waterloo 1815 Austrian Infantry and Artillery (they were on clearance sale). They are very disappointing, given how good their other products have been.