Here you can read about the different methods
Strengths, weaknesses, common fields of application etc.

Direct FFF methods	Tool inserts for plastic shaping	Tools for metal casting
Plastic	Injection moulding	Forms for single-use
SLA	Epoxy tool	Investment casting
Laser sintering	Metal spray tool	Plaster casting
FDM	3D Keltool	Sand casting
LOM	Cast Kirksite	Sand form manufactured with FFF
Inkjet	Laser sintering
3DP	MetalCopy
Metal	Plastic casting	Permanent forms
Laser sintering	Silicon moulding	Laser sintering

If you are searching for a vendor of tool inserts for plastic or metal parts, you can usually reach these through service bureaus. For master parts, often SLA or inkjet is the best choice and a manufacturer of these methods could be a suitable entrance.