Hi Tony,
The CAOS group site is a good source for design ideas
https://spectroscopy.wordpress.com/fibres/
but the tough bit is sourcing/making a mirror with the end of the (typically 50um) fibre embedded in it. I think most amateur built fibre fed spectrographs have ended up using the Shelyak guide head
https://www.shelyak.com/produit/pf0008-f-6-50%C2%B5m-injection-unit/?lang=en
Cheers
Robin