I'm guessing you will want to be working with numbers larger than 64-bits, and so you probably want GMP (see this page). This library is used by much of the software that number theorists use. (Magma uses parts of it, and PARI/GP uses it too.)

Note that GMP has a built-in function that tests primality by running several Miller-Rabin tests. It doesn't have a function that allows you to specify the input base, but that could be easily created by copying part of the source code.

Finally, note that the website factordb.com maintains a list of numbers that pass a surprisingly large number of iterations of the Miller-Rabin test before failing one. This list might be useful to you, and Arnault (in "Constructing Carmichael Numbers Which are Strong Pseudoprimes to Several Bases") gave an example of a 397-digit composite number for which the smallest strong liar is is $307$.