You just woke me from a slumber, totally rusty now.
Havn’t tried these but you can check these out:
Demos are available for download.
PIANETA MUSICA: musica e informatica su misura! PIANETA MUSICA: musica e informatica su misura! EAW: Software > Smaart Acoustic Tools Digital Sound Level Meter
Also few years back seen some serial/usb interface based spectrum analyzer on display in Pragati Maidan from a Taiwanese manufacturer costing @Rs4800/- It had a feature to measure SPL, not sure on there availability in India.
Hope this helps.