On: I was a teacher for 17 years, but couldn't read or...

[sampo]

I only searched for 'th' in the beginning of the word. We can add these to the previous result:

triathlon, smoothie, maybe also apartheid

Also the dictionary finds huithapeli, häthätää, rustholli, but I don't think these have 'th' as a phoneme.

https://www.kielitoimistonsanakirja.fi/#/*th*?searchMode=onl...

[tuukkah → sampo]

Nice new findings in the dictionary!

What do you mean by having 'th' as a phoneme? If you mean the sound "θ", I don't think any of the words are pronounced with one in Finnish, typically. Rather, they have a "t" sound followed by a "h", or just a "t".