One of the cheapest instruments to maintain on the Bell47G-3B1 was the Slip Indicator, you need a ball of wool, a pair of scissors and some Cello tape!
A really lovely aeroplane to fly and a good basic trainer too. Would have thought some of the ex British Army ones were still about? A call to Westland Helicopters, near Yeovil, may provide you with some information as they built the Bell under licence.