There are in fact some suitable lamps, but for the scratch builder they are very costly indeed. Indicator/brake/sidelights work out at about £10 per thousand at cost, yet similar items are sold by major retailers at a cost of £1.00 per 4 which according to my lousy maths is a little over a twenty-fold profit.
I would imagine that the headlamps available (2 for £1.00) have a lesser margin.
The chap who ventures to produce superior lamps is brave indeed. I offer my hopes for success on this venture.