I'm in the process of putting my flare-related spectrophotometry and files and codes online - the process I follow is outlined breifly in Schmidt et al 2014b, but has been expanded on as I've continued to work on flares. Essentially, the goal is to figure out how strong a flare is (in flux units) when given a magnitude or a difference in magnitudes. This is most often accurate when Everything so far is focused covers M0 to L8 dwarfs.
For now, the only piece online is the construction of quiescent SEDs. I use a combination of the SDSS optical spectroscopic templates, spectra pulled from the Spex PRISM and IRTF Spex spectroscopic libraries, and thermal emission to estimate the SED from 3000A to 12000A, a range which covers photometric bands from U and u to z, y, and J. Please note that the flux from 3000A-5000A may only be accurate within an order of magnitude - this is typically small compared to the flare flux, so it does not impede flare flux estimation.
The SEDs can be found in qSED/txt/. Please note that to use these SEDs in any published work, you should cite all the works used to put them together - collected in the .bib file.