In the Dungeon Master's Guide it gives you a matrix for character saving throws but I can not find the matrix for monster's saving throws, where can I find this?
On the same page as the character saving throw matrix (DMG, p. 79) is the heading:
II. SAVING THROW MATRIX FOR MONSTERS
The section doesn't actually include a matrix, so it's easy to miss when doing a visual scan; rather it has a four-point explanation of how to figure their saving throws, the first point being that they use the same matrix as for PCs.