I noticed Kevin, G6FOP posted in the forum of a company he found called Aerial-Parts of Colchester. They can be found online at http://aerial-parts.co.uk.
The company is run by John, G4ZTR whose experience spans more than 30 years of VHF and UHF contesting, DXing and DXpeditions. This experience is now being applied to a selection of engineering solutions to ham radio aerial / mast construction and installation.
They sell a wide range of antenna related products. Some ready made, some for you to build your own.
They sell power splitters for 144, 432 and 1296. You can also find mast clamps, bearings, element clamps, boom clamps, and fasteners of all kinds. They also sell aluminium although that is collection only.
Future products are listed as:
- Stacking frames for VHF and UHF aerials, built to manufacturers recommended dimensions, or to customer specifications.
- Directional couplers for VHF and UHF, uncalibrated.
- Alimast: a sectional aluminium lattice mast in 2.5m units, maximum height 15m.
- HF Verticals: telescoping for portable and semi-permanent use.