For anyone looking to buy alcohol fuel:

Inverness:
Craigdon Mountain Sports Inverness Ltd, 78 Academy St, Inverness IV1 1LU
Very near the train station
Stocks Bioethanol and Meths

Kingussie:
Service Sports, 26 High St, Kingussie PH21 1HR
Stocks Meths but may get some bioethanol for May


Service Sports said they'd also stock up on common items people may need for the TGO so worth a visit if you're passing.

The outdoors shop in Kingussie is run by Mike and Chelle.

I bought boots at their store last year and Mike was great to deal with.
[Mi]Chelle was not around that day, but I am sure she would be equally accommodating. The service I received at the shop was top notch.

Their address is:

Highland Sports Service
26 High Street
Kingussie
PH21 1HR
+44 1540661228
info@highlandsportservice.scot