I wouldn't bother trying to source another 6C001E-6 specifically, as they're the most unreliable of the lot. A good 6C001E-7 (if you can find one), or a Retroleum NebULA replacement is the way to go.

I know it's not a lot of help to you now, but to anyone else, this is why I am on a one-man crusade to get people to heatsink their ULAs! *Especially* any ULA which is made in the Philippines (i.e. the ones without the little logo graphic on).

NebULA : http://store.retroleum.co.uk/zx-spectrum-chips

Infos about ULA : http://faqwiki.zxnet.co.uk/wiki/ZX_Spectrum_ULA

The ULA (Uncommitted Logic Array) is a chip which controls most of the interfaces between the Z80 CPU and peripheral functions.

The ZX Spectrum 16K/48K ULA went through multiple revisions and is either a 5C or 6C series Ferranti ULA.

On a ZX Spectrum 128, or ZX Spectrum +2 the ULA is the Ferranti 7K010E (later labelled Amstrad 40056)

The ZX Spectrum +2A, +3, +2B, and +3B use an entirely different gate array. See The Amstrad gate array

Sinclair also experimented with an alternative AMI SAGA chip in a special batch.

Failures : http://hardware.speccy.org/reparar-i.html