I have not seen Moskonfyt in stores, but it might be found at Home Industry outlets. In the meantime, here is a recipe:

Moskonfyt (Must Jam or Grape Syrup)
Ripe grapes
10 ml (2 teaspoonfulls) slaked lime per 5 litres grape juice

Remove grapes from stalks, place in a large bowl and crush. Cover bowl and leave till the grapes ferment- a couple of days.
Strain grape skins from surface, measure grape juice and add slaked lime. Stand for 30 minutes.
Skim and strain through a double layer cheesecloth or muslin.
Heat strained juice to boiling point and strain again.
Boil juice rapidly, skimming occasionally until it becomes syrupy.
Pour the jam into hot, dry sterilised jars and seal immediately.