The IL62 is still 'alive' at Cubana. There were two operational the last time I was in Havana, one departing to Caracas, the other arriving from Nassau. They also operate the TU204 to both of the above.
Cubana operates the IL96 weekly (Thursday) ex LGW. You may have more luck finding out when the IL62 is flying by talking to Mr. Vasquez, Cubana Station Manager at LGW.