The leases are filed in the county courthouse, so you can find them there. Not sure if they have an online service. I pay for a subscription service that finds them. If a memorandum of lease is filed, you will only find the grantor and grantee and minimal information, not the royalty percentage.
Phoenix Capital has the majority of the leases from the last 36 months, but only shows a memorandum of lease. Kraken Oil and Gas is listed at 19% which could be a pure 19% or might be a rounded amount for a 3/16ths lease which is 18.75%. Purified Resources has leased at a listed 17% which is pretty close to a 1/6th lease which is 16.66666667%