vertical 4x4" and 4x2" --- 12" to 24" long ---- raised bed edging --- source help

vertical 4x4" and 4x2" --- 12" to 24" long ---- raised bed edging --- source help
I have a raised bed area that is framed and retained by 4x4" and 4x2" posts adjacent to one another. These vertical posts could be 12" to 24" long and sunk into the ground to form the raised bed. The ends are beveled on all 4 sides at both ends. They are pressure treated. . They've been in the ground for 20 years now and are starting to rot away. Before they get much worse it would be easier to replace them now. Since it's been a while since I took one out I'm not sure if they are 12, 18, or 24" long or if there are different lengths available. But I can't seem to find them at the local garden center. I could make the rounds at Lowes or Home Depot to see if they have them? Does anyone here recall seeing them recently at a home center, do you know any special name or manufacturer of them, are they available online? I can't seem to find them on line, perhaps these are no longer sold anywhere? I have found similar in round timbers, but it would be more effort to change it over. With more effort I could cut them from 4x4's and 4x2 but I rather not. The 4x2 are used to curve a section, straight long beams would not work in my situation.
any hints would be appreciated.
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