Not sure if the manufacturing drawings do still exist, but certainly under the current conditions of the Museum Workshop, there is no chance of having the parts manufactured "in-house". For a start, they do not have the equipment to produce such items, nor do they have the workforce (specifically trained to operate such equipment). As a volunteer in the workshops, I do hope that when the new workshop has been completed, that the Museum heirarchy will have the sufficient forward thinking to have an engineering workshop on site, the opportunities to bring much needed finances into the museum offering engineering services for manufacturing parts, or indeed, offering a restoration service "ie... "Have your vehicle restored at the home of the Tank" would be financially beneficial to the museum, even offering a shot-blasting or painting facility i'm sure would bring in much needed money for the Museum funds (and then they can re-invest some of that money into restoring or keepin the running fleet mobile).