Cross border securities transactions can only be derived with significant uncertainty using the CPIS data. The CPIS currently collects end-June and end-December position data. Flows are defined as the difference between beginning- and end-of-period positions; flows reflect changes that are associated with a) transactions; and b) other flows. The latter cover changes that are recognized analytically under three broad sub-categories: other changes in volume, revaluations due to changes in exchange rates, and revaluations due to other price changes. The CPIS does not contain information to distinguish between transactions and other flows.
The CPIS dataset can be found here.