PM: Here's what I can glean:
"The H-3 was assembled at Aviolanda. Subassembly took place at Aviolanda which built the fuselage and at Kromhout which built the engines. Fokker, a subcontractor to NHI, built the rotorblades. Final assembly took place at the newly opened Rotterdam Airport. The initial production run counted ten helicopters of which the first three were used for development, testing and airworthiness tests. The second production run of ten helicopters was undertaken by Aviolanda after Kromhout left the joint venture. This second production run was to be equipped with an uprated ramjet. It is unsure whether the improved ramjet was ever produced."
And ..
"Overall, nine H-3’s were built between 1958 and 1959 by NHI at Rotterdam Airport when Kromhout was still a parent company. After Kromhout left, Aviolanda built another two H-3’s at their Papendrecht plant. The few production models were mainly exported to Israel, Germany, the UK and the Dutch East Indies. A few models stayed in the Netherlands."
So I guess you can take your pick but, it seems around 20 or so.
Must dash .. trying to catch the New Year's Day concert live!