I have a particular source/sourcetype ; is there a way to know (through SPL) to get the name of the forwarder from which this particular source feed is coming?
You may not be able to find the forwarder name in all cases.
If the data is being forwarded via universal/heavy forwarder and you're not overriding the 'host' metadata, the host would be your forwarder. (index=x sourcetype=y | stats count by host)
If the data is being forwarder via universal/heavy forwarder but host metadata is being overridden, and you're forwarding your _internal logs from UF/HF to your indexers, you could find the forwarder name in the metrics log (index=_internal sourcetype=Splunkd component=MEtrics group=per_sourcetype_thruput series=yourSourceType | stats count by host)