I suggest that looking for calculator ICs is not going to lead to particularly fruitful results. The ICs used in low cost calculators are designed to be completely self standing and run on one battery cell. The interface to such chips is via the key pad matrix pins and a multiplexed display interface designed to directly connect to an LCD. The circuitry and software required for an 8051 to effectively interface to one of these things quickly becomes a large project. [Altho I grant that it would be a very good learning exercise!!].

In days of yore there as a chip from AMD called the AM9511 Arithmentic Processing Unit but it most likely hard to find these days.
Mike Karas