Just in case you already have a perfectly good mobo and only need the SATA ports, we have a spare used RocketRaid 2720 if it's of any use.  Datasheet: Datasheet_RR2700_V1.00_21_03_02e.pdf

This would come with a mini-SAS to 4x SAS/SATA cable with molex power connectors.  The image below shows the type of cable and its connectors.

If the OP is not interested, this is available to others.  I had $50 delivered nationwide in mind.

We also have a new-in-box HP 600732-B21 or 598657-001 "SATA to mini SAS cable" without the power connectors for $50 delivered separately or $40 with the card above.

Large numbers of SATA ports are becoming rare on modern motherboards.  An alternative I use is that any motherboard with two M.2 sockets can use one socket for its boot/system M.2 NVMe SSD and have an M.2 to SATA adapter board installed in the other socket to get more SATA ports.  I have two of these:

https://www.aliexpress.com/item/1005005427076687.html

You should be able to get them cheaper than that store though - they have gone up since I bought mine.  To find them, search for "m.2 sata adapter asm1166" on aliexpress.com.  There are other chipsets used as well, but the ASM1166 is the one you want.  The M.2 adapter with 6 SATA ports and ASM1166 chipset uses 2 lanes only of the 4 lanes of an M.2 NVMe port, and uses PCIe 3.0 for the connection.  So if your motherboard has an M.2 port that only provides PCIe x2 (but has a PCIe x4 physical connector), you can use that.  Or the BIOS may sometimes have an option to take 2 lanes from an M.2 port and give them to another PCIe port.  Or it may automatically take 2 lanes away from an M.2 port when another PCIe port is in use, or when motherboard SATA ports are in use..  With the ASM1166 chipset, the 6 SATA ports will support full speed for all modern SATA hard drives (up to 270 Mbytes/s these days on recent enterprise drives) at the same time.  If you are using SATA SSD drives, then you will need to do the calculations as to how many of the SATA ports can be used at fuill speed at the same time.  You can get adapter boards that have 8 or 9 SATA ports, but then you can not run them all at full speed at the same time.  But that may be fine for what you want to use them for.

Another alternative is to get a SAS adapter card and SAS to SATA cables for it.  You will frequently need to install SAS to SATA firmware to make this work, which is a fiddly operation and not for someone who is not technically inclined.  You then need a PCIe socket with enough lanes to run your chosen SAS card.  The only SAS boards that are reasonably cheap are old PCIe 3.0 cards, but they need a PCIe x8 or PCIe x16 slot.  If you pay lots more you may be able to find a PCIe 4.0 or 5.0 card that will work in a PCIe 4.0/50 x4 slot.  The faster SAS cards would likely support 16 or more SATA ports, where the old ones will support up to 12 (6 per SAS port), but will not run all of them at full speed at the same time.  But the small motherboards you are looking for will likely not have enough or suitable PCIe slots.  I have two LSI SAS2008 based PCIe 3.0 cards and they work well in older motherboards that have more wide PCIe slots to put them in.

IME they have stopped putting mass sata ports on mobos because they get disabled when a m2 or lower PCIe slot gets used in many cases, causing support issues.

I have an old GA-F2A88XM-D3H with CPU and RAM if you are interested. 8 SATA connectors.

I'll have to turn it on to confirm CPU but pretty sure it has 16Gb RAM.

EDIT: In the time it took me to find it and check..... :-)