Needle bearings are generally used because of a lack of space i think (or at least, greater width than height), you are not likely to be able to uprate these bearings to something more solid.
http://simplybearings.co.uk/shop/needle_roller_choice.php?gclid=CLDAs_T0oLoCFbPItAodlh0AKQ
Bushings (as in shock bushes) are used because they take very high loads, and dont turn more than a few degrees (think of the amount of rotation at the shock/frame interface)
so i would suggest you could either:
find the bearing size, and just keep swapping it out at regular ish intervals (10 to 15 quid a bearing)
OR, if you know of a machineist, get someone to make you a bushing mount. A steel sleeve in the bearing hole, a steel sleeve on the bolt, and a gap the right size between the two! To take a betd hula hoop (3 quid each)? your ride might not be quite as smooth, but it should last a good while, and be a 15 second job to swap out.