If the Seat tube is a bigger diameter than the seat post then some sort of shim / sleave could conceivably be used but as the seat post appears to be over 7mm wider there is nothing you can do - it is not going to fit. It is the Seatpost @ 33.9 and your frame seat tube is 25.4 correct?
Your best bet will be to sell the 33.9 and buy a 25.4mm OD seatpost - Thomson make (or used to make) an Aluminium 25.4mm in their Elite range. Otherwise you may have to use one of those chromed steel types that cruiser bikes come with. Most modern steel bike seat tubing is made for 27.2mm seat posts which also won't fit your frame so it may be tricky to get one
Possible but then it most likely will be a custom job. It making a coupling with one end that has a inner diameter 33.9mm and the other end with outer diameter of 25.4mm. If you know what I mean. But you might have to cut your 33.9mm post till very short to accomodate the coupling. But then for that effort and cost? Just go buy a 25.4mm post.
If you are not looking for anything expensive and don't mind them quite heavy your best bet will be local shops that sell / repair market bikes - they are more likely to have that size than shops selling high end road bikes and the like. BMX's use 25.4mm as standard but most of them are sold very short and have a pivotal saddle mount so probably won't work with your bike anyway.