Websites for landcontracts, not to my knowledge. Other than going through MLS listings(some realestate agents websites enable you to view all mls listed properties), or use a real estate agent, or you looking through craigslist even to find them.
Lookup "utica and marcellus" these are different shale gas plays currently in eastern parts of OH, most all of WV, and western PA.
see map
Different areas see different production numbers, and types of gases vary also on locations. But those maps will give you a general idea.
Some things to think about / research. (Oil&Gas is my career field btw)
Does the property have gas rights (gas like coal or other minerals could have been "reserved" by a prior owner, which means they keep the rights to them and all you may get is surface rights) Make sure you run a mineral title, in addition to the real estate/mortgage title. This applies regardless if you go through a bank or land contract.
It may have existing production (means gas rights would be "held by production" by whatever gas company had leased and drilled the property in the past. Sometimes companies will keep a gas wells going even if it's just barely producing, just to keep the gas rights they have under lease. This will allow them to return and drill at deeper formation in the future.
For instance my x-gf's grandfather owned 120ac in Cambridge area, a shallow gas well (doesn't require much acerage) was drilled in 1950's and is still going today, barely. But that company still has rights to drill more wells anywhere in the 120ac tract until production ceases. All about negotiating the right lease and he could have avoided that and had maximized the potential of his acreage.
"IF" you can get mineral rights, and get it in the right areas. You can literally pay off the property by leasing the gas rights. When you lease, your paid a "delay rental". In past these were broken down to yearly/quarterly payment. Presently this is usually paid in full, 60-90 business days after a signed lease and mineral title ownership is verified. I've seen $6000 per acre during some fierce turf wars between gas companies for prime areas. (prices have come down a bit though, all depends on location, maybe as low as $250 per ac)
Then if/once gas well is drilled your paid a royalty ranging from (1/8th) 12.5% up as high as you can negotiate it. Depending upon how much production the well makes, it can be very very lucrative. So it may be best to grab a larger piece then you had intended.
"the most valuable thing in the world is land, because God isn't building anymore"
Thats just some of the basics, I could go on for awhile on this topic.
PM me when time comes and I can give you a hand with anything O&G related.