I just purchased some Nathan AirChime K5LA’s for $500. The gentleman i purchased from told me these were K5LA’s that he purchased new from Hornblasters about a year ago for around $1,300 and he only used for 3 months. It has bells 1,2,3a,4a,5 and everything seems to be working. The manifold has an upside down 30115L. I can see where a manifold tag plate once was but has been removed unfortunately. Also, the back of the bells all say 30109. Sorry for how dirty they are they’re covered in diesel soot. Trying to determine value, rarity, collect-ability, ect.
I think you’ve found most of your answers on the H&W Board 
The only thing I might add - If they were purchased new from Hornblasters then you’ve most likely got the OTR “Over The Road” edition of the K5LA because Micro Precision through their resellers (e.g. Hornblasters) does not sell railroad edition horns to anyone other than RR manufacturers. It could be the reason why the tag was removed off the manifold. The earlier versions had a restrictor in the base of the manifold. It’s probably long been taken out but check to make sure.
I think $500 for a K5 is pretty OK. If it sounds good then happy days.
Welcome to the forums. They’re air hungry so get a good compressor system.