I searched the IFHF's online database at ROOTSIRELAND.IE. It contains abt 19 million B/M/D records for MOST Irish counties. This includes Roscommon. Surviving Roscommon B/M/D records started late and are somewhat scarce.
I found a 1 B record for a John Dillon B 1840 (exact) in Co. Roscommon. However, the recorded father's forename is Richard, and mother's is Mary. Very doubtful if these are for your ancestors unless some of your info is incorrect.
Suggest you visit the IFHF database, register (free), do your own searches, and wait until the IFHF notifies you as more records are added.