Ive broken the uni(?) joint on my uncles old set up and not sure what parts I need to fix/replace it. Couldn't find anything that looks similar to this anywhere.
If the bits on either end of the orange bit unscrew, then its a 'boge joint'. They are still available and a lot of windsurfing shops still have them. I have no idea about the threads or whether they were a standard or not.
If it's ancient it will probably break straight away. Try and unscrew the short blue bit from the white pulley device, and the plug from the yellow bit.
As mentioned the yellow thingy looks like a standard boge joint, and a new one will last several years.
You may need to use heat on the nuts/bolts if locktite has been used.
It looks similar to a tyronsea fitting.
Like formulanova sail, get a boge joint. The threads should be compatible. Worst case scenario get a new mast base with an hourglass/boge universal joint and fit the white bit (on the right hand side of top picture) to the bottom. Will be fine (unless plastic itself is kangaroo edward).
Clarence