It's a bit hard to say for sure. Both Vegeta and Goku have their moments of strength. Goku has some unique powers and techniques that give him an edge at times, but Vegeta is no slouch either and constantly works to catch up and surpass Goku.
Generally, Goku still holds the edge over Vegeta. Their power levels fluctuate, but Goku often achieves higher peaks of strength and unlocks more powerful forms first.
The availability of K manga depends. You could check major online retailers such as Amazon or specialized manga websites. Sometimes, it's even available for free on certain fan-run sites, but be cautious of the legality and quality there.