Data on how the number of sidecar funds are not easy to find.
Based on some membership data from the Angel Capital Association, my best guess is that around 10% of angel groups that are part of ACA have a sidecar fund. Groups in the ACA tend to be the larger and more established groups, so the proportion of all collective angel efforts is probably lower. So perhaps 5% of angel groups have one, meaning around 50 in the US?
What about in the southeast? As with much in early stage tech funding, the southeast does not lead the pack. However, it’s pleasing to see several groups in the region with a dedicated sidecar fund. Not only does VentureSouth have one (actually three!), there are several university affiliated groups in North Carolina with dedicated sidecar pools from various university and alumni sources, plus others around the Triangle, Atlanta and in Florida.