Mast Manufacturers

Selden
Now offering a sleeved 2420 section Mirror mast which is widely regarded as being more flexible than a Superspars M9. I understand the stiff lamda section mast is no longer available.
Superspars Superspars M9 section continues to be popular. More recently they are offering a Mirror mast using their MHA section (Holt "Aldebaran") which is more flexible than M9
Sailing School and Rigging Sell booms & spinnaker poles. Run by Craig Bond who has 30 years of experience with Mirrors at the very highest level.
Trident-UK Trident-UK manufacture a Bermuda mast which can be dismantled into 2 pieces so you can still stow it in the boat for trailing etc. Trident also still manufacture Gunter masts (alloy tube with wooden end plugs)
Collars If you want an traditional wooden Gunter mast (i.e. all wood, no alloy tube), Collars based in Oxford should be able to supply one.
Goldspar
Australian based, uses a 50mm tube for a bottom section with a spun conical top section. Sadly Goldspars stopped dinghy mast production in 2018.
Hawk Marine Products
Manufacturers of Needlespar masts. I understand (2019) that Hawk Marine Products have now stopped production.
Z-Spars
Made by Craig Bond when he worked for Z-Spars & popular with sailors from Brightlingsea. They were a round tube with a taper above the hounds, anodised black with a rivetted on track. They were pre-bent to the maximum allowed under the rules. Sadly no longer available.