They should be available from the usual suspects (DBE, r.d., JAE, SJSportscars, Kelvedon, Lotus Supplies, etc.). I would buy the bolts from one of them. Moss has hundreds of thousands (millions?) of MGs, Triumphs, Jags, Austin Healeys, Sunbeams, etc. These guys have a few thousand old Lotus. (Lotus has decreed that the plural of Lotus is Lotus.)