Well the primary evidence is:
- Regulations in Jacobite armies making clear that the obligations of leaders to maintain armies primarily meant supplying them with flintlocks;
- British records of arms seized or amnestied following Jacobite defeats; and
- Tallies of weapons recovered from dead Jacobites on the field of Culloden itself; 750 dead Jacobites were individually counted, and only 200 broad swords.

This generally accords with the fact that every victory delivered increased quantities of British weaponry, and of course thousands of guns were delivered to from France and Spain (whose advisers were certainly not teaching the recipients of those guns how to fight with broad swords).