A TW225, good for you! I am pretty sure the engine has much more in common with the TW200 than the 125. Then in turn, the 125cc and 200cc engines have many parts in common, but I wouldn't buy a 125 for spare parts, especially since the 225 is probably newer, I doubt you would need to replace much in the near future. Parts are not so hard to find anyway.
Why don't you post a picture of your rarity?