There is NO SUCH THING as "substitute" MEK.
Solvents suitable for thinning Butyrate Dope include Acetone, MIBK, Ethyl Acetate, MEK, and Toluene. Those are listed in quickest to slowest drying (evaporation) rate. They can be used straight or mixed in any proportion to achieve the drying rate desired.
Virtually any Home Depot or Lowe's carries Acetone and MEK unless in California. They used to carry Toluene also but do not any longer. You can get Toluene at Sherwin-Williams paint stores.
Ethyl Acetate and Toluene are available at most independent hardware stores.
TSC stores and Family Farm and Home stores carry MEK as well.
MIBK is available at some large industrial supply stores and chemical warehouses, as well as eBay.
Lacquer Thinner from DuPont/Nason or PPG at automotive paint stores will work due to being free of Methanol. Hardware store lacquer Thinner WILL NOT WORK due to always containing Methanol.

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When in doubt, WHACK the GAS and DITCH the brake !!!

Yes, there is such a thing as NORMAL, if you have to ask what is "NORMAL" , you probably aren't !
Failure may not be an OPTION, but it is ALWAYS a POSSIBILITY.
ALL systems are GO for MAYHEM, CHAOS, TURMOIL, FIASCOS, and HAVOC !