Kevin:
Welcome to Ireland Reaching Out!
First, Suirville is a townland in the civil parish of Relickmurry and Athassel. The corresponding RC parish would be Golden/Kilfeacle.
I searched the subscription site FindMyPast and located baptismal records for two sisters to John--Ellen and Margaret. See below. Here is a link to the Golden parish register. https://registers.nli.ie/parishes/0267 You can scroll thru the register and see if you can find Johanna. Note the baptismal records start in May 1833 so there is always the possibility that Johanna was born before May 1833.
The surname Mullen is mainly a Northern Ireland surname although the surname is also found in good numbers in Galway and Cork. Not many in Co. Tipperary. Likely James is from another county and he and Johanna met in America.
Let me know if you have any questions.
Roger McDonnell
First name(s)MargaretLast nameRyanBirth year-Baptism year1843Baptism date07 May 1843ResidenceSuirvilleParishGoldenAlternative parish namesGolden and Kilfeacle, KilfeacleDioceseCashel and EmlyCountyTipperaryCountryIrelandFather's first name(s)ThomsFather's last nameRyanMother's first name(s)MargtMother's last nameO'donnellRepository
National Library of Ireland
National Library of Ireland registerhttp://registers.nli.ie//registers/vtls000632729#page/1/mode/1up
First name(s)MargaretLast nameRyanBirth year-Baptism year1843Baptism date07 May 1843ResidenceSuirville
ParishGoldenAlternative parish namesGolden and Kilfeacle, KilfeacleDioceseCashel and EmlyCountyTipperaryCountryIrelandFather's first name(s)ThomsFather's last nameRyanMother's first name(s)MargtMother's last nameO'donnellRepository
National Library of Ireland
National Library of Ireland registerhttp://registers.nli.ie//registers/vtls000632729#page/1/mode/1up