Can I get OFFCL_CODE field using Com API?

Historical reasons. This field has been part of real-time data record for decades since before fundamental & reference dataset even existed within what was Reuters then. Today you can also retrieve data contained in OFFCL_CODE field from fundamental & reference dataset using DEX2 library and fields TR.CUSIP, TR.ISIN etc.

OFFCL_CODE cannot be retrieved using DEX2. The content of OFFCL_CODE varies by RIC, but most commonly this field contains CUSIP or ISIN, or SEDOL, or another security identifier. These security identifiers can also be retrieved using DEX2 and fields TR.CUSIP, TR.ISIN, TR.SEDOL etc.