1. Alignment is sth. that requires big shop equipment; it is not a DIY job.
2. Are you sure that shop you have been to told you that they need to install some shims to adjust the rear wheel toe? If you are sure, they do not know what they are talking about. At Toyota dealers they do not use shims to adjust toes.
3. Your 2000 Sienna rear wheel toe adjustment does not need any extra parts; only adjust the tie rods, provided that it was not suffered from a side impact in an accident.
4. It is an easy job to adjust your van's rear wheel toes back to within the specs by just adjusting the tie rods. Why don't you bring the van to a dealer to do a 4-wheel alignment for about the same amount your shop tries to charge you?
Good luck.
