I did a search and I couldn't find the answer to my question so I'll ask here. Specifically, I'd like to know the Mopar P/N for the standard OE "low pressure" (red) oil pump relief spring for a big block oil pump. Everything i've seen on the internet and here on Moparts is the high pressure spring info. Thanks in advance for any help you can provide.

I don't think the low pressure spring is available for consumers. We used to have a source at Melling who would sell us 10 at a time but once he retired we lost the ability to buy them. I pull them out of stock engines and save them.
It wouldn't be a difficult part to reproduce but I've never seen anyone sell them. Check with Hoffman. If anyone has bothered to reproduce it Hoffman would.

From my 1969 parts book:
383, 440 - 1737742
426 - 2406677
I don’t know what the color is, just the part number info. I searched it on Arizona Parts, and it said red, standard spring.

The standard red oil pump spring is the stock pressure, I don't think Mopar or anyone else ever made a " low pressure " oil pump bypass spring.
You can cut or grind the end of the spring down to reduce the overall length which will lower the oil pressure some
Why do you want low oil pressure?