I'm wrong! Except for Reform, they all have MPs, and these parties do too:
- DUP
- Sinn Féin (but abstain)
- SocDem and Labour
- Alliance Party of NI
en.wikipedia.org/wiki/2019_Uni…
That's pretty impressive for a FPTP system. They're all miniscule compared to the top 3 though. All smaller parties together have fewer seats than the SNP.