your message is a little short on detail. When you say "some" of the wires are "starting to fray", what exactly do you mean? Which "some" wires? How frayed?
Most of the MacGregors I''ve seen have nicropress fittings at the terminal ends of the standing rigging which are easy enough to replace yourself, but I tend to associate this type of fitting with dinghy rigging. A more long lasting alternative is swaged or mechanical (Norlok, QuickAttach fittings), the latter you can also do yourself.
Depending on the age and condition of your boat, if "some" of the standing rigging is ready to fail, it might be best to replace all of the standing rigging. I believe there is also an outfit in Cape Cod (macgregorparts.com) if you don''t want to cut wire and attach fittings yourself.