The free ways to get troops are daily summon, summons token ( silver color ) and epic troop token ( gold color ).
Only epic troop token ( gold color ), has a chance of 4* troops. Based on RNG you could go months or years without a 4* Troop. Once you get a 4* Troop, you could go decades without a rainbow set of 4* troops.
Generally 3* lvl 10 troops = 4* lvl 1 troops and 3* lvl 20 troops = 4* lvl 11 troops so I would concentrate on your 3* troops for now.
Notes
Math
Two epic troop tokens a month
10% chance of a 4* Troop
20% chance of a 4* Troop per month
X tokens for 99% chance
( 1 - 0.2 ) ^ x = 0.01%
0.8 ^ x = 0.01
X = log ( 0.01 ) / log ( 0.8 )
= 20.63
= 1 year 8 months
Check
0.8 ^ 20.63= 0.1
Out of 10k players
100+ will go 10 months without a 4* Troop
2% chance of a green 4* Troop
4% chance of a green 4* Troop per month
X tokens for 99% chance
( 1 - 0.04 ) ^ x = 0.01%
0.96 ^ x = 0.01
X = log ( 0.01 ) / log ( 0.96 )
= 112.811
= 9 years 4 months
Check
0.96 ^ 112.811= 0.01
Out of 10k players
100+ will go 5 years without a green 4* Troop