If you are going to roll your own ARM, check it out!
To have your own custom ARM chip could be very expensive, if you are going to approach the ASSP SoC IC design service and push the chip to via foundry. Here we are talking about custom SoC design based upon ARM and FPGA. Here you can consider following suppliers.

Combining logic, memory, and a processor core, Altera created the industry's first embedded processor FPGA solution that allows engineers to integrate an entire system on a single device. Altera's processor portfolio includes Excalibur™ devices that offer integrated processor subsystems and the configurable Nios® embedded processor for Altera® FPGAs.

The V5IP-7000 is a complete ASIC/SOC logic emulation, prototyping and IP development/verification system. The V5IP-7000 base board is populated with one Xilinx Virtex-5 LX330 FPGA, supporting peripherals, IO, and power distribution. Up to six additional LX330 (or LX220) modules can be plugged into the high-speed connectors of the base board to significantly extend the platform's FPGA gate density.

The V5IP-7000 platform is designed to support AMBA AHB 2.0 and 3.0 AXI for ARM926EJ-S, ARM1136JF-S, ARM11MPCore, and ARM1156T2F-S Core Tile. These modules can be stacked on the based board or/and FPGA add-on LX330/LX220 modules.

In addition to the ARM add-on Core Tile modules, the "Video (DVI , Cameralink)", "PCIe/Cardbus ", "Debug (Mictor Logic analyzer", and " ADC/DAC 4CH ADC (125MSPS)" modules are also available to further extend the flexibility and functionality of the V5IP-7000 platform.

Atmel's CAP™ is a microcontroller-based system-on-chip platform with fast local memory, a wide range of industry-standard peripherals and interfaces, and a Metal Programmable (MP) Block that allows the designer to add custom logic. By combining the performance, density and low power consumption of the fixed portion of the device with the flexibility of the MP Block, CAP enables application-specific products to be developed in a fraction of the time and at a fraction of the cost of standard cell ASICs, but at a unit price close to that of standard cell devices. Atmel's CAP is based upon ARM7TDMI and ARM926EJ-S cores.

Actel is taking the design of real-world systems to a new level, offering designers the capability to quickly implement their applications using the industry's only ARM-enabled, mixed-signal FPGA. In addition, Actel has put in place an expanded design infrastructure to support the single-chip ARM-enabled Fusion devices, which contain the soft ARM7 processor CoreMP7 in a version of Actel's award-winning, mixed-signal Fusion Programmable System Chip (PSC).

A Chinese doctor candidate announced his own ARM7 clone IP on opencores. However on web page, the detail will not be revealed until some issues are sorted out.

After implementation these soft-core or hard-core of ARM processors, you can either put them into foundry service after some clean up, (it sounds easy, actually not) then you can have your own ARM SoC business.