Do you want one of their models they sell or a system ready to go running truenas?
I have a Supermicro 846 (24x 3.5") or SuperMicro 216 (24x2.5) and can put dual xeon motherboard with ram from 64gb to 512GB in it, or a single E5 xeon with 64 to 256GB or a lower power Xeon E3 v3 with 32GB RAM, 846 with a single SAS2 or SAS3 + cable to expander backplane the sc216 if you go with a E5 xeon could do single SAS2 or SAS3 for expander backplane, or multiple SAS cards to non expander backplane. I can also have the software installed on an Intel SSD (or mirrored SSDs). You would need to supply the capacity\storage drives.
For 4 drives I think I may have an Atom board left with RAM + a 4 bay hot swap chassis that fits the ITX motherboard.
If any of that sounds like what you're after send mea PM.