Contemporary parts always on Fleabay for not much money. Can you post a photo of the bike, particularly of the lugs and top of the rear stays ? It would help with tentative identification. Have you looked for any numbers/markings on the rear drop-out? Plain numbers, of up to 7 digits, without letters, seem to have been used on most common models between 1968 and 1972, so it is likely that your bike was made in that period. ANY Carlton is worth saving if the frame is sound.