Found a great selection of St. Patrick's Day bonuses.

Slotastic Casino
Players can receive a 217% bonuses using bonus code STPATRICK20 with a minimum deposit of $25. In addition making a deposit in March can get you 17 free spins on Lucky 6 slots using bonus code PADDY2020

BitStarz
Try your luck and receive 100 free spins on Four Lucky Clover using bonus code PATRICK
Expires March 17, 2020

Konung Casino
On March 17th only receive 17 free spins on Leprechaun Goes Wild with minimum deposit and bonus code SPS20

CryptoWild
60 free spins are available with a minimum deposit of 0,006BTC on Lucky Lady's Clover. Receive 30 free spins with minimum 0.003BTC

Bao Casino
Players can receive 50 free spins each day from March 17 - March 22 when using the daily promo codes.
March 17: patric
March 18: luck
March 19: cheers
March 20: gold
March 21: bigwin
March 22: rainbow

Spy Slots
Players that qualify can celebrate St. Patrick’s Day spinning an exclusive Mega Wheel/Reel and win 50+ free spins on Leprechaun Song, Kiss Me Clover or Irish Luck. Use bonus code LUCKY - March 17 only

Crystal Slots
Players at Crystal Slots that qualify can also celebrate St. Patrick’s Day spinning an exclusive Mega Wheel/Reel and win 50+ free spins on Leprechaun Song, Kiss Me Clover or Irish Luck. Use bonus code LUCKY - March 17 only