At the Bolton Show yesterday I managed to pick up the Premier Components Catalogue and I notice that they have several GC-related items.
Loco Frame kits including coupling rods and, for outside cylinder engines, connecting rods. LNER classes O4, B4 (Immingham), D10/11 (Director). The frames are made from 1.2mm profile milled brass and screw together. Requirements for pick up holes and plunger units should be given with your order.
Tender Frame kit: Robinson 4000 gallon tender.
Coupling rods (profile milled nickel-silver). LNER classes A5, D9, D10/11, B4, B5, B8, C4/5, O4. Normally these are supplied in rigid form, but can be provided jointed at extra cost.
Premier Components also supply excellent three-link and screw couplers. 'Excellent' in the sense they are robust and pre-assembled, not necessarily for extreme accuracy to prototype. These have become my standard fitting.
There are also various detail items in the catalogue that may be useful - Wakefield Lubricators for example.
Premier Components are at 14 Swanlow Avenue, Swanlow Park, Winsford, Cheshire, CW7 1PB. Their trading arrangements are unusual. You just send for what you want and they send it back with an invoice for you to pay. I hope such trust is not abused.