Hi,
Thank you so much for your interest in our products and for using our community.
For S32K146 you have 128KB as SRAM and also you can use 4 KB of FlexRAM for use as SRAM too. Additionally, such S32K1 derivative do not have External memory interface (Please refer to Feature comparison section of datasheet).
So your best option is to upgrade to another S32K1 derivative, like K148.
Hope it helps you.
Have a nice day!