Need to match old 5/4 x 3.25 T&G floor boards

So the problem is the current deck boards on my screened in porch measure 5/4 X 3.25. The only T&G boards I can find at my local mill are 5/4 X 3.125. The gap will be too big for me to patch in where the rotted boards are. Aside from just milling my own, does anyone have any work arounds for this situation? Is this a common issue when working with older houses (1940s)?

If I do need to mill my own, what type of wood would you suggest for this exterior screened in porch? Just fir?

Thanks!