Can I obtain another kitten to live with our two year old cat? Will they get on together?

It depends to a certain extent on the individuals involved, with some cats being more tolerant of company than others. Almost inevitably at first, your established pet will resent the intrusion of a newcomer into its home, so try to avoid potential flashpoints, and feed the cats separately.

It is also vital to keep your kitten's immunisations up-to-date, because the older cat will be wandering outside, potentially leaving the kitten more exposed to illness than if it was living on its own. It will probably be better to obtain a female kitten if possible, because there is less likely to be conflict in the future as they grow up.
At worst, the cats may studiously avoid each other, but hopefully, they will settle down together and become close companions, even to the extent of grooming each other on a regular basis.