So at my table the general house rule is, if you want to do something a little outside the rules you can, as long as 1) you're not doing just for mechanical advantage and 2) you can come up with a good story. We're starting in Uther's time of course, following the great campaign. My mental image of my character is firmly built on the idea of a vary large knight wielding his iconic two hander, which will become a family heirloom. I have the idea of taking it as a prize initially, and perhaps having that first blade be the inspiration of the eventual production of great swords. So. . . who do I have to kill to get one? Someone that I can survive fighting for preference. Alternately of course, receiving it as a gift or reward works as well, but that seems like it would be from a faerie this early.

My best idea so far is a smallish giant, to whom his sword is a normal sized but to a knight would be huge(ish). Any better ideas, or a suggestion as to where to look?

There is a table somewhere (I think with the Badon tables - might be in book or Army) that lists different saxon tribes using different 2-handed weapons. One of them I believe uses a 2-handed sword.

So that could be a good place to get it from, or from a small giant as you said. "small giant" is one of the options when fighting the Saxons.

A chance meeting with a Thracian with an rhompaia? See https://en.wikipedia.org/wiki/Rhomphaia.

I think the Faerie idea has greater potential than the small giant one.

I don't see a particular problem with introducing an individual Great Sword early. It is expensive and less than effective in comparison to sword and shield combination, but it is impressive, and as you said, iconic. It shouldn't be past a swordsmith's skill to make a longer bladed and hilted sword.

Many of the 'advances' in the weapon technology came about since the circumstances mandated new weapons. A warhammer wasn't rocket-science, but until plate armor came about to general use, it wasn't necessary.

Oh, just make sure that your GM (and yourself, too) is aware of the fact that the Great Sword will NOT break a Sword on a tie. This was an unfortunate omission in 5.1 edition, and has been errataed by Greg. The bit in p. 174 should read: "unless it is a sword or a great sword as well."

Reference here:
http://nocturnal-media.com/forum/index.php?topic=1877.msg12834#msg12834

Thanks for the various advice. If going the faerie route, any recommendations as to what to throw out there? I'm not looking for a cool "I win' magic sword here, more like a cool one on one fight that would make a knights reputation. I'm thinking a single combat that would give the sword, a good name for the sword, and a fitting title. The knight is currently known as the Bear of Idmiston (defeated the bear solo in the intro adventure). Seems kind of generic though, so I'm hoping for something better to come from this fight. Assuming I survive it

The redcap is a really cool Faerie monster which wields a great weapon (a halberd according the the write-up in PGC but a pike according to the english wikipedia-article). The one in PGC will slaugther a whole group of PKs, but there might be a redcap that isn't that though. It would be a cool fight and would give the sword a nice backstory.

And if I was your GM I would add a twist. One day the redcaps kid shows up, howling with hate and demanding "his" sword back. Or something more subtle. ;D