"Fore" is not an adjective or adverb, but rather a preposition meaning "in front of" or "before". Comparatives are used to compare two things, and "fore" doesn't describe something in a way that can be compared.
For example, you might say:
* "The car is in front of the house." ("Fore" is a preposition here.)
* "The car is farther ahead of the house." (This uses the comparative "farther" to compare distances.)
Let me know if you have another word you'd like to find the comparative form of!