Hi,
Most of the extra Z180 features are in fact peripherals in the IO ports , in the range 00-3F, so you can code your own macros
in tour favorite Z80 assembler.
There are a few moreinstruction on Z180 wrt Z80 , like for sleep mode and multiplication , you can deal with macros as well.
Zilog should have Zmasm , but masm or as80 can be found anywhere , i mean this is not warez , hitech has let it free iirc.
I have have plenty of assembler but i am not sure i can send you any.
I like a lot this cheap Z80 emulator , with also nice features for programming asm and basic ( basic compiler included ) , dissassembling , etc ...
www.oshonsoft.com/z80.html
I bought it and has always a shortcut to it on my desktop! great value !
instead you can google for as80 , zmasm , ...
maybe this link can alsohelp :
www.gaby.de/z80/z80sdt.htm
cheers,
-Leo