The valve spring part number is 90501-32022. The exhaust and intake valves use the same spring. In North America, that valve spring is specific to the ST165 USDM & CDM All-Tracs. It was widely used on JDM engines beyond just 3S-GTE's, so you may find some stock in Japan - try Amayama.com.
Otherwise, will have to find someone with an ST165 3S-GTE head or whole engine they are not using anymore.