The preposition avik/avek is used for both instrumentals and comitative.
The postposition ashichi and uschi (both from Cree) is used for both instrumentals and comitatives by a few speakers.
A verbal prefix wiichi- 'to do something together' can be used for comitative but not for instrumental.
Source: Fleury 2007
Source: Laverdure and Allard 1983: 37
Source: Fleury 2007
Source: Fleury 2007
Source: Laverdure and Allard 1983: 232