I was thinking about wargaming the first Carlist war in 6mm, but there are no ranges for this period and there seems to be no straightforward options for any proxies, especially for the Carlists with their red berets. 

Any suggestions? The Isabellinos should be largely able to be done with the Napoleonic Spanish range. 

Milliput a bit of cutter and maybe prussian landwher...

Here's what someone else did for Carlist berets a decade ago:

[TMP] "6 mm Carlists" Topic

Or the former Irregular Miniatures WWI Chasseurs Alpins might work:

GWF12 (O) 1915 Chasseur Alpine/Tonkinese tirailleur in beret (3)

Does Baccus have any line infantry that wear a beret or similar?