Unless it has been chemically/heat treated or irradiated the spores of moss (and mushrooms) will maintain their vitality almost "indefinitely". Samples have been restarted from herbarium specimens 200 years old.
The main culprit of moss death and failure to start is poor water. Moss MUST have sodium free, neutral water or "rainwater". Tap water, mineral salts (fertilizers), etc will all kill it back so if aiming for lush moss you must be very sparing with ferts IF using them at all (1/4 or even 1/8th strength) with plenty of flushing with distilled after wards. Using Urea Free orchid fertilizers such as Gro More will help in not killing your moss, CPs or other "no fertilizer" plants.
So there are several ways to jump start mosses:
Long Fibered Sphagnum Moss
Taking two handfuls of DRY Long Fibered Spahgnum Moss (the brick of blonde stuff they sell for Orchids and Carnivorous Plants). Grind the two handfuls against each other over a pail, this "mills" it quite finely. Then wet it with distilled or R/O water let it soak up all it wants, then squeeze it "dry" (meaning as much as your hands can sqeeze out). Place it in an even layer about 1 - 2" deep into a Jiffy Greenhouse seed starting tray with the clear cover, mist every day or two, keeping it well moist & humid but not waterlogged and floating. Make sure it gets light, a cheapie 20 watt under cabinet strip light in daylight spectrum lain over the clear cover will do to provide light and warmth and maintain a high RH inside the Jiffy greenhouse. It will grow sporadically at first but after about 90 days you should start to develop a nice field of green. this can be harvested in sections and "diced" (use a sharp knife and cut it up like wet chives or something). These pieces can be sprinkled as an "innoculant" for your tanks and the moss will do it's thing from there provided it has light and moisture (daily misting & constant high RH). Replace harvested areas with more ground sphagnum. You could also do a thin layer of this all over the floor of your vivarium.
Carpet Moss/Frog Moss/"found moss"/ etc.
For other kinds of dried moss it's best to grind the hunks of moss to a powder or close to it, mix it with enough beer (yup ale!) to make it into a pancake batter consistency. Using an old paintbrush "paint" it where you want it. Mist these areas very gently for a couple weeks/months and maintain high RH and you will find that you have moss just where you want it. For a ground cover using this just "splatter" it by shaking the soaked brush over the ground, it will take root and spread of it's own accord.
When you are grinding up ANY of these mosses wear a scarf or tee-shirt over your nose & mouth. It isn't good to inhale the moss dust as you can inhale bad spores, the grinding of the moss is what releases the spores in the dried moss and ensures far higher germination rates than simply keeping a clump of dried moss wet. But grinding also releases anything else in there too. Keep whatever it is out
of your respiratory tract!
I must add these method also yield interesting "hitch hikers" by way of seeds and spores in the dried moss. I've gotten phosphorescent orange mushrooms, skinny blue/grey mushrooms, a sundew carnivorous plant(!), liverworts, and numerous types of ferns which will start as little heart shaped plates, then often develop their stipe hairs, then the first fronds. Anything that pops up "grassy looking" is just sedge grass so pluck that out when it rears it's ugly head, it lives through roots so get rid of it early!
Hope these give you some ideas!