Hi Nathaniel,
The collection spoken of speaks to me as a whole, more as Thai in full context and it also coincides with other spears and polearms known in the same vein that are definately Thai. In particular, although not unique to Thailand, materials used such as the type of bamboo shafts and types of collars are good pointers. Even a number of the longest and highest end examples I have seen of quality Thai spears are on sturdy rather unrefined looking bamboo shafts. What I have also noted though and more so in Iain's link provided, is that these pieces in the Palace museum seen to have more refined timber shafts and a standardised type of collar
..maybe a regional thing, maybe a military thing, maybe a royal thing???
IMHO only, the consistancy of design traits at this point in time, along with similar blade stylings seen in the context of the collection, points to this region for me.
As Spears of SEA are a rather unexplored, I for one would love to see more work done on the subject....if the weren't so expensive to ship I'd be buying more, I love them long pointy SEA spears ;-)
Gav