Center Speaker matching Front Speakers

My HT is 5.1 setup.
My sitting room is 14LX12Bx8H (normal English home). I have 2XIMF TLS 80 Transmission Line Speakers ( about 1976), Onkyo TX-NR609 Receiver, small 1XYamaha Front and 2Xsmall Yamaha Rear speakers. I have a small Yamaha Sub but I do not use it.
Reading various posts, center speaker should be matched with the 2 front speakers. I feel my center is ok but not as good as I would like it to be.
How do I go about finding a center speaker that will match with the fronts with spec as this:STUDIO TLS 80

Free Standing with Plinth; 38 1/2" x 16" x 18" wide

Drive Units
Bass unit 11 3/4" x 8 1/4" flat polystyrene diaphragm loaded by transmission line
mid range unit 6" plastic cone containing in separate line
tweeter 1 3/4 " diaphragm
3/4" chemical dome super-tweeter

Electrical four way at 375 Hz , 3.5 kHz and 15 Khz

Frequency Range
20 Hz to beyong audibility

Matching Impedence
4 - 8 ohms (see graph)

Efficiency Measured via Pink Noise at 1 metre on axis for 40 watts

Driving Power Requirements
40 - 80 watts
I would be grateful for any suggestions.
Wow, that's a HARD one!  lol.  These things actually sound a lot like the classic horn loaded speakers of the 70's, like the JBL or Klipsch speakers.  If space is not an issue for center channel, probably the best way is to see if you can get a used TLS-50 or TLS-80.  There's one in ebay, local pickup only.  If you search on hifishark, there are a few in Canada.
Don't know what your budget it,  if you can swing $1000, you can get a new single Klpisch Heresey speaker.  The size is basically 24" high by 16" wide.  I think that's about your best bet for something "new" that would match -somewhat- closely to your TLS. 

Otherwise, you could try a new Klipsch Reference center channel to get a little bit of that "horn" classic tweeter (like R-52 or RP-400 or RP-500), but it's going to have a much higher resolution and will still sound radically different than your TLS speakers.
Hi auxinput,
Shame I had 2 TLS50s and got rid of them when I upgraded to TLS80s. I did not realise that center speakers need to have such high spec. Only now after reading posts I was made aware of it. Space would be an issue as wife has allowed these TLS80s after much negotiations!
I will have to look at much smaller units with enough spec to match the TLS80s. If you have other smaller recommendations I look forward to it.
I agree that a single TLS50 or TLS80 would be a good choice if you have space, however, any Klipsch speaker will not be a good match. The TLS80 is a transmission line speaker and not horn loaded. That 96db spec or 98db (what I found in an old brochure) is at 40 watts. The spec for 1 watt will be ~83db, so the high sensitivity of Klipsch speakers will be a huge mismatch. Getting the closest timbre match will be just a matter of trying different speakers. You might try listening to various pairs of speakers in retail locations and when you find something that sounds similar to the TLS80’s, buy a matching center for those.
Yeah, it's entirely possible that the receiver will not be able to correct for a 13db variation between center and left/right.  Good catch.