Best murine alpha-synuclein specific antibody to my mind comes from Cell Signaling item # 4179. A good pSer129 is clone AP1537Y. Clone 4D6 has higher affinity to alpha-syn aggregates (but does not exclusively show). A Campbell Switzer staining might help you as well, though I don't know in how far the aggreates in the Rotenone model are argyrophilic.
You can calculate with approx. 300g rat and admin volumes for i.p. that are rather at the lower range (you'd want to dose DMSO at the lowest limit, thus as low as possible for solubility). You can adjust the volumes to the current animal weight.
Are you sure you want to dose 1mpk or rather 1 mL per kg, since this is what Cannon et al suggest (2009, Neurobiol. Dis)? If the latter, then you are at 300µl i.p. injection volume of a 3 mg/ml Rotenone solution for rats. Since rats are approx. a third kilo in weight, then you are quite at 1 mpk :-) I'd still adjust admin volume according to current animal weight, since little change in dose can lead to different effect.