Maybe you know someone who has a collection of unused filters.

In reply to a post by MHC:

Older filters were good for ADSL but their high frequency characteristics were not optimised for VDSL although they would still work. Users may often see lower than expected results.

Hum, do you wish to explain how a low pass filter that works for ADSL is not optimized for VDSL given that VDSL operates at a higher frequency than ADSL? There must be some new laws of physics that I am not aware of.

I think that you need to check up on filter design.

It may be low pass but that does not mean it is perfect at all frequencies above that especially when they are cheap single stage. They can have effects on signal level and phase.

Having looked at some many years ago, we actually saw that one or two versions which actually had high frequency pass bands somewhere around 10MHz.

Just ring your ISP, when I moved I had done the same thing and I called BT, a day later I had 6 sent to me (bit of an overkill but thanks BT).

The micro-filter is there purely to prevent the DSL signal getting into the telephone where it may cause trouble. There is no need to filter out the low (audio) frequency phone signal from the DSL signal to the modem as the modem will do that very effectively.
None of the filters I have seen applies any filtering whatsoever to the DSL signal. That said, if the low-pass phone filter is not working properly then some of the DSL signal could be getting into the phone and being lost, which MAY make a slight difference to your internet sync speed. It would depend on the phone and the filter.
FTTC is no different to ADSL in this respect, both use the phone line for internet data, though FTTC uses more channels, at higher frequencies, to get the increased bandwidth.
If you do not intend to attach a phone then you do not need a filter at all and it would be better not to have one.