FamilySearch has the original documents microfilmed. You can view online and download. You need to know the year and diocese and the date. It is fussy to find the one you are looking for - a typical volume will have 100s of images, and there can be more than one volume for a year, but split into date sections like Jan - Jun. You can search for the actual marriage bond you want - either at the National Library of Wales - or at FamilySearch - which will give you the bare minimum - their names, the diocese, and the date. I prefer to use the Library of Wales search to find the basic transcript ,and if I then want to see the actual document - I have to go to FamilySearch.
Lindsay