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As Ted says, freeze the parts, if possible warm the swinging arm as well, maybe stand it out in the sun (if it ever comes out that is). Buy a long 10mm threaded stud bar, make sure it's longer than the swinging arm pivot tube AND the needle roller, thick washers and just pull the bearings into position, use a good fitting socket afterwards to sink them into the arm. Same trick with the rear bushes, they are easier to get in than out, if the stud bar is long enough you can pull them both in at the same time. . Protect your new paintwork from the washers by using some rubber etc underneath, something like a folded piece of inner tube.
Both ends that you can't get the collar through? Any visible damage to the bearings. I suspect you may have collapsed the roll cage due to hitting it, you can't drive them in, they must be pressured in.
Did you try doing both rollers at the same time? You could try emailing the manufacturer and explaining the problem and seeing if they'll sell you another pair of roller bearings.