You can still order memory similar to the one that you already have based on the part number. Also check on the link below for other compatible memory from Dell: [URL] 
Hi all, Currently, I have a T310 with 2x4GB of memory  DIMM details: (Hynix 4GB PC3-12800 DDR3-1600MHz ECC Registered CL11 240-Pin DIMM Dual Rank Memory Module Mfr P/N HMT351R7CFR8C-PB) I plan to add 4x4GB with a total of 6x4GB=24GB Will this new memory configuration be supported? Thanks for replying Please see more info about the server below; Server has 1 CPU (Xeon x3430 @ 2.40Ghz) Memory Information : Ok Attributes of Memory Array(s) Attributes;Memory Array 1Location;System Board or MotherboardUse;System MemoryInstalled Capacity;8192 MBMaximum Capacity;32768 MBSlots Available;6Slots Used;2ECC Type;Multibit ECC Total of Memory Array(s) Attributes;ValueTotal Installed Capacity;8192 MBTotal Installed Capacity Available to the OS;8192 MBTotal Maximum Capacity;32768 MB Details of Memory Array 1 Status;Connector Name;Type;SizeOk;DIMM_A1 ;DDR3 - Synchronous Registered (Buffered);4096 MBOk;DIMM_A2 ;DDR3 - Synchronous Registered (Buffered);4096 MBUnknown;DIMM_A3 ;[Not Occupied];Unknown;DIMM_A4 ;[Not Occupied];Unknown;DIMM_A5 ;[Not Occupied];Unknown;DIMM_A6 ;[Not Occupied];  Memory Device Information : Ok Memory Device on Connector: DIMM_A1 Attributes;ValuesStatus;OkDevice Name;DIMM_A1 Size;4096 MBType;DDR3 Synchronous Registered (Buffered)Speed;0.63 nsFailures;None  Memory Device Information : Ok Memory Device on Connector: DIMM_A2 Attributes;ValuesStatus;OkDevice Name;DIMM_A2 Size;4096 MBType;DDR3 Synchronous Registered (Buffered)Speed;0.63 nsFailures;None  System Components (FRU) Information Device;Serial No.;Part No.;Revision;Manufacturer;Manufacture DateSystem Planar (BMC);CN1374008602B7;02P9X9;A00;DELL;Mon Aug 09 04:00:00 2010Power Supply 1 (PS 1);CN1797208E0NQR;0N884K;A00;DELL;Mon Aug 16 10:25:00 2010DIMM_A1;4B55A111;HMT351R7CFR8C-PB;N/A;Hynix Semiconductor (00AD04B380AD);Mon Apr 09 16:00:00 2012DIMM_A2;4B15A14C;HMT351R7CFR8C-PB;N/A;Hynix Semiconductor (00AD04B380AD);Mon Apr 09 16:00:00 2012  
Dell PowerEdge T310 Memory Upgrade configuration