No. You will have to wait for a lot of time if you want all episodes in 720p. Rumbel subs release torrents in xvid and h264 but the h264 releases are 480p. Crunchysubs, which is I think the only group that has released Gintama episodes in 720p has just released and subbed only some of the later episodes. You cannot find all the episodes in 720p anywhere, you have to wait a lot of time the hd releases.
Episodes 130-201 are in 480p by Horriblesubs on animebyt.es Register at that website and you can get it. Even if all the episodes are/were released in 720p. They would be quickly uploaded on BakaBt, nyaatorrents and Animebytes.
Yes, you can find only a little amount of episodes in 720p over the internet.