They are mīs and tīs; so far as I can tell, they are found exclusively in Old Latin inscriptions (i.e. you won’t encounter them in archaic imitations of Old Latin designed by Classical authors). The more you know…
If anyone has further thoughts or resources on these, feel free to share below.
Yeah, I made that genitive up, but only to describe a real phenomenon in Latin! Some adjectives of likeness, nearness, and belonging that normally take the dative will occasionally take a possessive genitive. This transition is especially common where the adjective approaches the force of a noun.
Fuit hōc quondam proprium populī Rōmānī: this was once peculiar to the Roman people. (~a peculiar trait of)
Fuit semper amīcus Cicerōnis: he was always friendly with Cicero. (~a friend of)
Adeō patris similis es: you’re just like your master. (~a chip off the old block)
Here’s the full list of adjectives that perform this function—
aequālis, aequāle: of the same age (~a contemporary of)
affīnis, affīne: related to by marriage (~kinsman of)
aliēnus, -a, -um: belonging to another (~a stranger to)
cōgnātus, -a, -um: fellow-born (~kinsman of)
commūnis, commūne: common to (~kinsman of)
cōnsanguineus, -a, -um: sharing a bloodline (~kinsman of)
contrārius, -a, -um: opposite (~the opposite of)
dispār: unlike (dispar suī, in philosophical diction)
familiāris, familiāre: of close relation (~intimate of)
fīnitimus, -a, -um: adjoining (~neighbor of)
inimīcus, -a, -um: hostile to (~enemy of)
necessārius, -a, -um: connected with (~component of)
pār: equal to (~a match)
pecūliāris, pecūliāre: personal (~peculiar trait of)
propinquus, -a, -um: neighboring (~neighbor of)
proprius, -a, -um: personal (~peculiar trait of)
sacer, sacra, sacrum: holy (~holy with respect to some deity)
similis, simile: alike to (~spitting image of)
superstes: surviving (~survivor of)
vīcīnus, -a, -um: neighboring (~neighbor of)
Note that this genitive construction is actually more common for proprius, -a, -um than the dative construction.
Similis with the genitive is especially common with personal pronouns (meī, tuī, suī) and within the fixed phrase vērī similis (probable).