Seat back panel retaining bolts - Tuscan

[Speed 3]

One of the lower Allen head CSK bolts that retains the rear trim panel on the Tuscan / late car seats has gone AWOL together with its cup washer. Can't find it listed on any of the usual dealer parts sites. Anyone know what thread it is ? Looks like the cup washers may be a TVR special as they look cast rather than pressed and so have a flat base. Not too worried if I can't get an exact match on that but the bolt does need to be right.