The Oakeshott Type XIa is a hard one to pin down. It was created by Ewart Oakeshott to attempt to classify a couple of swords that he felt were essentially Type XI swords in overall shape and design, but with a slightly broader, and often slightly shorter, blade.
As we know, Type XI swords were an early medieval Cavalry sword, designed primarily for cutting down lightly armored opponents from horseback on the battlefield with its extra reach. The Type XIa was, it seemed, used in the same manner, though the stouter blade would have made it effective in the thrust as well as the cut, and was perhaps the most versatile of the two - though surviving examples are very rare, and it does not seem to be a particularly popular type of sword. A trend that continues with modern reproductions.
The parent type XI swords are quite under represented on the fully functional sword market. But to find a replica Type XIa is seemingly a fools errand.
Most of the high end sword makers who concentrate their efforts on producing historically accurate replicas have at least one example of each of Oakeshott's sword types. But to date, none of them have made a Type XIa..
Now quite often, entry level sword makers - more or less 'accidentally' - have at least one or two swords that fit any given sword in the typology. But the problem with XIa is that most swords that might possibly be classified as one are probably more likely to fit the XII category (for, as we know, many sword collectors live by the mantra 'when in doubt, it is a type XII!').
MyArmory has an excellent in depth article on Type XI swords here which
explains their history and lists some high end reproductions and images
of actual antiques, including some XIa.
And of course, you can - and should - read more about these swords and all the others in the Oakeshott Typology in his book, Records of the Medieval Sword
I hope this information on Type XIa swords has been helpful. To return to Oakeshott Typology Made Easy from Oakeshott Type XIa Swords, click here