74SHU04 in a Marantz CD-7

Hi,

looking at the schematic of the Marantz CD-7 I see on page 17, the DACs, they use two 74SHU04, QD21 and QD51.
This appears to be an 6 Pin Inverter.

I cannot find any details of this IC, no datasheet (it's just an Inverter, don't really need to see it), no-one seems to have any for sale, none on eBay etc etc.
Just curious as to why this IC is no longer available.
I realise 74HCU04's are readily available and only one of the 6 can be used or all in parallel I am just curious.

P.

(Link to the Manual :- ( https://www.hifiengine.com/manual_library/marantz/cd-7.shtml ) )