Please find a list of websites below offering Perpetual Mass enrolments. This list is under construction so please feel free to forward any recommendations:
http://holysouls.com/office/ (This site offers free enrolment)
https://franciscanmissionassoc.org/enrollments-devotions/perpetual-enrollments/
https://msf-america.org/ (This site offer Perpetual Masses for $10 & Gregorian Masses from $200)
http://www.knocknovena.com/
https://www.aidtochurch.org/
https://www.mscmissions.ie/product-category/occasion/
https://www.omvusa.org/ways-give/masses-memorials/perpetual-mass-enrollment/
https://www.ourladyofangels.net/perpetual-mass-enrollment-for-deceased/
https://mymassrequest.org/Request-A-Mass/Perpetual-Mass-Enrollment
https://www.kilteganfathers.org/folders/
https://www.atonementfriars.org/graymoor-spiritual-union-enrollment/
https://www.littleflower.org/perpetual-deceased-mass-card-/
https://www.littleflower.org.uk/pages/appeal/category/mass-cards
https://www.holycrossusa.org/support-our-work/holy-cross-association/perpetual-prayer-enrollments/
https://www.nationalshrine.org/enrollments-devotionals/shrine-prayer-guild/
https://www.missionofsacredhearts.org/masses-and-prayers/mass-enrollments/
https://www.marian.org/enrollments/cards/Divine-Mercy-Perpetual-Enrollment/448/144/RNO/SEO/PERPB
https://the-shrine.org/product/perpetual-enrollment/
https://myfranciscan.org/worship/perpetual-enrollment/
https://www.xaverianmissionaries.org/support/
https://www.irishpallottines.org/perpetutal-mass-enrollment/
https://shop.glastonburyabbey.org/Perpetual-Enrollment-Cards-s/1814.htm
http://www.salvatoriancenter.org/devotional-items/mass-enrollment-cards
https://www.companionsofstanthony.org/pray/mass-enrollment-cards/
https://servite.org/prayer/enroll-in-pma/
http://jesuits.ca/supportus?RTN=DONATE-20150109033422
https://redemptoristsdenver.org/st-joseph-mass-league/
https://secure.oblatesusa.org/p-1623-perpetual-enrollment.aspx?source=M21IGI0PE
https://www.bluearmy.com/mass-association/
https://www.canons-regular.org/perpetual-mass-enrollment
https://sacredheartretreathouse.com/memorials/