3560X & 3750X series switches only support "Cisco Flexible NetFlow" that too only on their Uplink module ports
Specifically the command "ip flow export" is not supported as its mentioned in the "Unsupported Global Configuration Commands" section of 12.2(58)SE configuration guide:
http://www.cisco.com/en/US/docs/switches/lan/catalyst3750x_3560x/software/release/12.2_58_se/configuration/guide/swuncli.html#wp1054584
Documents for future reference:
** Cisco Catalyst 3750-X and 3560-X Series Switches Q&A
http://www.cisco.com/en/US/prod/collateral/switches/ps5718/ps6406/qa_c67-578933.html
** Datasheet
https://www.cisco.com/en/US/prod/collateral/switches/ps5718/ps6406/data_sheet_c78-584733.html
The new Cisco Service Module offers enhaced security and Flexible Netflow (FNF) features on the uplink ports of the Catalyst 3750-X and 3560-X. The service module is supported with IP Base or IP Services feature set. It can be used with SFP or SFP+ at 1G or 10G speeds. The new Cisco Service Module has custom dedicated hardware for FNF monitoring, separate from the dedicated hardware for MACSec. Therefore there is no impact on packet forwarding performance & latency. It offers flexibility with the user being able to define flows.
** Getting Started with Configuring Cisco IOS Flexible NetFlow
http://www.cisco.com/en/US/docs/ios/fnetflow/configuration/guide/get_start_cfg_fnflow_ps6441_TSD_Products_Configuration_Guide_Chapter.html
