looking for twyford syphonic air extractor _ original part?

have a twyford WC set, but need to replace the air extractor part. have tried an imitation, but it doesn't work/flush right, nor lasts for very long. the set is 37 years old. i am located in the caribbean which became the problem with sourcing the part. agents are unable to find as well, or be of any assistance.
1) can this part be found? am willing to purchase and ship, but part must be original. found one sold by "cronexrabo", but that turned out to be another "look alike", and didn't do the job very well.
2) should i just replace the tank if unable to find?
3) or due to this being a whole different system, replace it all?
any advice would be welcome.