Hi mate sorry to hear that your knock is back, but you really have to get it professionally diagnosed.
The bottom ball joint on the front suspension is part of the compression arm and is not available separately as an oem replacement.
The ARB links are available either as stock or adjustable.
Guessing which part is giving you grief is extremely expensive.
I have most of the suspension arms and ball joints available as preowned.
I also have available new stock ARB links and new adjustable links, the latter should be fitted when you have a lowered suspension set up.
Best to get an expert to check your suspension over mate and get an informed diagnoses.
I have about a 25 full sets of these available with next day delivery, so no problem with supply.
Alex.