LPC4357JET256 as ARM® Cortex®-M4/M0 LPC43xx Microcontroller 32-Bit double core with 204MHz clock, 1MB (1M x 8) FLASH in 256-LBGA (17x17) from NXP our closest replacement, is this possible alternative from the same manufacturer for requested 500 pieces as LPC43S20FBD144E LPC43XX 32-BIT RISC MICRO CONTR ROMless Obsolete Marketplace MCU in 144-LQFP (20x20) shipping in approximately four days via Rochester Electronics LLC.
Sorry, the lead times for any ARM® Cortex®-M4/M0 LPC43xx from NXP are still very high.
Please review the datasheets to ensure the alternative will work for your application.