As a seasonal bartender at WDW and a Trader Sam's weekly regular while completing my degree in California, I might be able to offer some helpful information here.
I have the current Cocktails A to Z recipe guide for Disney bars (last updated in 2008), and it does not have the Lapu Lapu. Some of the older recipe Rolodexes found behind some of the WDW bars have old Disney recipes, such as from Pleasure Island and the old Top of the World. It is possible the Lapu Lapu might be found in one of those Rolodexes, but I highly doubt any bar at
Disneyland would have one because the standardization of beverages between WDW and DL bars is relatively new, with DL moving in a direction away from the generic bar menu found all over WDW. But, if you really want a Lapu Lapu as served at the Polynesian, tell any bartender what goes in it, and they will make it. It's an easy recipe that all Disney bars are stocked to make: Myer's Dark rum, 151 rum, pineapple juice, orange juice, and sour mix. The bartenders will know the proper ratios. Of course, none of them carry hollowed pineapples, so it will come in a regular glass.
On the other hand, if you have never visited Trader Sam's before, I recommend trying one of their unique tiki drinks. Their menu was designed by an outside beverage consulting firm, adapted from traditional tiki recipes. If you want something similar to the Lapu Lapu (rum, little less sweet), then I recommend the HippopotaMai-Tai. It's not as tart as the Lapu Lapu, but it's not overly fruity like the Krakatoa Punch. If you want to set off one of the effects, then order the Krakatoa Punch, Shipwreck on the Rocks, or Uh-Oah.
The Trader Sam's bartenders also know some off-menu tiki drinks, my favorite being the Navy Grog, and a few know how to make both versions of the Kungaloosh. A couple of the bartenders - Kelly and Michael in particular - really know their tiki drinks. Michael used to manage the bar at Don the Beachcomber's in Huntington Beach, and he can make you Don's version of the Lapu Lapu, which is not at all like the Polynesian's Lapu Lapu - it's much better!