Evohome with M28x1.0 TRVs

[jdp80]

Having moved and taken all the TRVs with us I've discovered about half the radiators in the house are fitted with older "Orkli" valves which apparently have a M28x1.0 TRV fitted

I have found one place stocking an adapter but at £13 each the cost soon adds up!

Any alternatives other than replacing the actual valves?