Countries that buy old, used aircraft carriers don't often buy state of the art new aircraft fleets at the same time, and often don't buy new aircraft at all.
That's perfectly true. I was merely pointing out that it was feasible to buy Buccaneers up to the middle of the 1970s.
One possibility is that the British sell some of their own Buccaneers along with the aircraft carriers and use the proceeds to buy a batch of new aircraft. Which is unlikely but possible.
Another unlikely but possible scenario is that the British sell their whole stock of F-4K Phantoms along with the aircraft carriers and use the proceeds to buy some new or used Phantoms with J79 engines as the RAF doesn't need the extra performance or shorter take off and landing characteristics the RN needed to enable the Phantom to operate from its aircraft carriers. The Phantom was still being built in the USA at this time and in the 1980s the RAF did buy some used F-4J Phantoms from the USA. I repeat its possible, but unlikely.
However, I think the idea of Ark Royal and Eagle being sold to another navy in the 1970s is unlikely in the first place on the grounds of their age and condition. The required equivalent of the American SLEP/FRAM refit needed to keep them operational for at least another 10 years would be prohibitively expensive.
I also think that the only possible candidates for buying the ships are Argentina, Australia, Brazil, Canada and India.
IMHO Australia and Canada are the least likely. The OTL RAN and Maritime Command were simply too small to absorb even one of the two ships. IIRC Ark Royal had a crew of 2,640 in the 1970s, which is the equivalent of 7-10 destroyers with a crew of 200-250. It would only be feasible if Australia didn't cut back its defence spending at the end of the Vietnam War and Canada didn't cut back its defence spending from at about 3.0% of GNP in the middle 1960s to 1.8% of GNP by the late 1970s. Even then I think it would be very difficult to recruit and retain the extra sailors needed to keep both ships operational.
Argentina and Brazil are more feasible. IIRC their navies had more personnel in the 1970s than both Australia and Canada. They also had an aircraft carrier each in the 1970s anyway both of which had a crew about half the size of Ark Royal in the 1970s (admittedly so had the Australians) but they also still had one or two of the 2 Brooklyn class cruisers acquired in the 1950s so the surviving ships could have been paid off prematurely to provide some of the extra crews. Also they had conscription so it would be easier for them to have for them to recruit more sailors. It would also help that both countries were under military dictatorships in the 1970s. Plus Argentina bought 2 Type 42 destroyers and Brazil 6 Vosper-Thornycroft frigates in the 1970s so TTL the sale of the ships could have been part of a larger package.
India with it's massive population could have easily recruited the extra men needed for these ships without paying off any of their existing ships if the Indian Government was prepared to spend the extra money. I think they would have kept Vikrant on as a training ship or converted her into a helicopter carrier. What is needed here is the military need and political will to do it.