I have a 54 plate Forester 2.0 turbo 5 speed manual. 

The rear diff is real noisy and l was wondering if diffs off of other models would fit? 

Many of them will fit but you need to ensure you maintain your ratio (unless you deliberately want to change). You have probably got an R160 rear diff but I wouldn't know the final ratio. Have you tried ebay and breakers to source a replacement? Also when was the last time you replaced the oil in the diff itself?  

A quick look and it appears you may have the 4.111 ratio. This was specced for Euro vehicles and had a matching 1.081 ratio transfer drive reduction gear. Other countries had a 4.444 diff but that was matched to a 1.000 transfer reduction gear (in gearbox)

I would confirm the diff you have and then use that to search, then it becomes model independent

A quick cross reference based upon a pdf sent to me (thanks @savage bulldogs) if it is indeed a 4.111 ratio look at early Imprezas and and legacies - but not all models again across the years and models there were different ones used - A quick check on evil bay searching using 4.111 has generated some results so you will just need to confirm which ratio yours has

While the right ratio diff will fit from differing model I would make effort source a used XT diff as plenty XT models getting broken and from parts reference the diff part number shows only used in forester so it likely had some minor design differences .
You likely find a rear diff on ebay for anything from 80 to 180 quid if keep an eye out for something likely be decent order . they pretty easy swap out, do be sure it diff not wheel bearings or mix of poorly matched tyres.
subaru awd likes matching tyres in brand/model and wear, bad tyres = noises and eventually viscous diff faults .
Never understand why people want a awd yet will run **** tyres on them ! 🙂

Where can I purchase a reconditioned Differential, to replace my very noisy one. Any ideas on cost?

some on ebay currently - used not recon