How to find a deck sealant that is compatible with some old sealant that I can't find anymore
According to your link, they sell this strictly at Lowes in Canada. I'm assuming you're not Canadian as you're using the .com instead of the .ca link for Lowes:
https://www.lowes.ca/exterior-stain/olympic-378-l-wood-protector-toner-stain-and-sealant_g1346222.html?searchTerm=Olympic-Wood-Protector-Honey-Gold-Toner-Exterior

In terms of mixing, don't. You'll waste a perfectly good can by mixing an older batch with questionable quality and an impossible to replicate colour (assuming it properly mixes). 

Here are the potential situations: throwing away 20$ of stain, or spending your time applying 60$ worth only to find out you have a patchy deck/doesn't adhere to the surface forcing you to clean it all off and buy another 60$ worth followed by applying it. They could blend, but is it worth the risk?

In terms of a hand spray application, if you go with another product/brand check the labeling as some strictly avoid spray application.