If it's a CF1 (alloy top engine) then you're out of luck. I sourced a Chinese firm that still makes them.. but haven't heard back from them after trying to contact them and they have no UK distributor. I suspect these parts might be unlicenced copies..
Autolusso makes a silicone equivalent... It's a bit dear... but it's the only alternative to duct tape at the moment.
If your idle is lumpy it's more likely to be the Idle Control Valve... (that black knobbly bit on top of the throttle body).
Unbolt it (2 screws).. Don't lose the little paper gasket (or make sure you have some gasket goo to make a new one). Inside there is a little metal wheel with a slot in it, that turns depending on manifold pressure. Get a match stick or cotton bud, some WD40 and some carb /electrical contact/brake cleaner.. and *gently* wipe away the black soot and gunge in there until the wheel moves freely.
Yes it should be metal coloured, not black.. and yes it should rotate. If yours is sticky, work it gently to free it up. Clean it as much as possible using the WD40 and cleaner solvent to dissolve the soot.. give it a lube with the WD40 and then re-fit it. Teh idle will be much improved.
CF2/3 plastic top engines have a different ICV .. a bit more complicated and (I think) less likely to gum up but I have no experience of these. If you remove the ICV I recall you have to do something to re-calibrate it.. though not sure why, logically. It's just an electrical component at the end of the day.. but anyway research that some more before you dismantle it..