Getting here is very easy indeed – National Cycle Route 7 passes by the bottom of the railway embankment (so there’s a good footpath from Killin, Balquhidder, Strathyre, Lochearnhead – take your pick!)
The high gate doesn’t appear to ever be locked. I’ve been up here twice now and both times there was no lock. It’s a popular walking route too so access seems possible at all times.
Walk along the railway embankment until you reach Moth’s “metal framey-sheltery-type structures” (actually cattle feeding units) and go through the gate here behind them. Once through turn right amongst the tress and there is a large mound in front of you, next to the burn. The cairn is on top of this mound.