Random number between two numbers with "gaps"

I am trying to generate random numbers between two values. I am using, vba for this, so that, the way to do It would be:

Int((upperbound - lowerbound + 1) * Rnd + lowerbound)

But because of the particular situation I am in, I need to exclude numbers from the middle of the sequence, so for example I need numbers between 50 and 100 and I need to exclude 80, 50, and 77, for example

So to do this, I wrap the random number generator in a Do While loop, and check if the number is one of the excluded numbers, and if it is, I keep generating numbers.

This brute-force seems to me inefficient and I am not sure about the statistical properties of the sequence if I do this,

are there more elegant algorithms to accomplish this task?

thanks in advance