Just looked on RS and ISSI do make a 256k part, IS62C256AL:

http://uk.rs-online.com/web/search/searchBrowseAction.html?method=3Dretriev=
eTfg&Ns=3DstockPolicy_uk|1||new_uk|1&Ne=3D4294960712&Nr=3DAND(avl:uk,search=
Discon_uk:N)&N=3D4294612429+4294611775+4294743309+4294610474&binCount=3D121=
&multiselectParam=3D4294612429%204294611775&selectAttribute=3D256KBit#bread=
Crumb=20
<http://uk.rs-online.com/web/search/searchBrowseAction.html?method=3Dretrie=
veTfg&Ns=3DstockPolicy_uk%7C1%7C%7Cnew_uk%7C1&Ne=3D4294960712&Nr=3DAND%28av=
l:uk,searchDiscon_uk:N%29&N=3D4294612429+4294611775+4294743309+4294610474&b=
inCount=3D121&multiselectParam=3D4294612429%204294611775&selectAttribute=3D=
256KBit#breadCrumb>

--=20
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