I've always understood it that following a Chaotic Deity does not necessitate being outright "Lawless" yourself, at least not when they are also Good. You can go that route, sure, but even the most Chaotic of Good Deities have certain codes and beliefs they adhere to, thus making a Paladin quite possible to build based upon those tenets. They just need to focus on upholding the Good side of things, and making it possible for the Chaos (vis-a-vis "personal freedom of others") to be able to flourish in a positive way. The drawback is they can never fully commit to that way of life themselves, but that is the sacrifice they make in order to allow others to enjoy it.
And soooo...
I see your Paladin of Desna, and I raise you the racial choice of GNOLL Paladin of Desna! :D
Yes, I have in fact run a Gnoll Paladin of Desna. While this might seem like a completely counter-intuitive character choice at first, considering Gnolls are typically followers of Lamashtu (The CE Deity directly opposed to Desna), there are always exceptions to the rule. Not all members of a particular race are necessarily Evil - outliers can and do exist. Admittedly this particular outlier has taken his particular outlier-ness to the extreme, but I did my best to fit his story to the setting and I think I did a passable job of it.
In any case, it's made for a fun and very driven character so far, with a fanatical devotion to destroying the cult of Lamashtu (mirroring Desna's own devotion to this cause), coupled with the irrepressible wanderlust of your typical Desnan adherent (which in no way clashes with being a paladin - after all, it allows him to quest perpetually!). It also gives him the complication of having most of his own race branding him a traitor (quite literally) and wanting him dead. It's one of my most successful and fun characters to date. :)
If it interests you at all, I actually published his back story some time ago on DA, complete with character picture. I hope it's ok to post external links? http://nadermadcat.deviantart.com/art/Jangral-Gnoll-Paladin-of-Desna-284421 371
Anyway, to sum up, my stance is that you can have paladins of virtually any deity (and race!), but it's down to how you fit their back story to the setting, and more importantly in how you roleplay them which decides if they're really effective or not. There is always the increased risk of a fall as they struggle with their unusual circumstances, but I think that just makes them a lot more interesting to play! (And touch wood, Jangral has not fallen... yet)