long answer: you could go with a variation on the wind chime tek and dangle that thing upside down to get the liquid out, but that’s probably one of those REALLY Bad Idea’sTM
edit: double check that none of those other ports have dip-tubes, and also check they didn’t give you a port on the bottom.
The only other place i know of (at least use too) is open source steel and i would absolutely no buy there’s. I did and the dip tube was half welded, your best bet for best quality is @Soxhlet
I’ve got some 1.5" triclamp x 1/2" fnpt diptubes × 48" Length. You can throw on a 6" Lid with a 1.5" Port and cut the diptube to length. I’m not sure where to find a 6" Lid with welded diptube. However you can always order a 6" lid and some 1/2" tubing and take it down to a local welder.
First turn the tank over and look at the bottom, if there is an buldge the dip tube goes there which is probably one the side hook ups not the middle
Take picture of the bottom the tank. I almost bet it’s one those side hook ups not the 6inch…that just needs splate or sight glass rated and it’s for getting in there to clean it
I had to play the “whats in stock” game to make it work for ya, but this is how you could add that diptube. A bit ugly, but you have enough ports for your Pressure gauge/PRV setup, and an n2 assist/recovery pathway (Or you could just cap them seeing as your tank already has other places for that)… I did not finish this for you, so add the necessary parts which are easily accessible and in stock