aliexpress has the clamp-type thermocouples. But @xulfiqar's suggestion of buying rubber clamps should do just fine, and cheaper too.
Now I'm thinking what kind of store would keep rubber clamps and how to explain it to the shopkeeper.... 
What xulfiqar and afnan said beforehand...you need to give us pressure readings like I've done HERE. You don't necessarily have to post a picture but you should note down the pressure readings (ideally make a short video) when under following conditions:
1) Note down ambient temperature (use digital thermometer, place it 1-2ft in front of the front bumper but don't touch it's measuring bulb/surface with anything, just suspend it in air). You'll also need to take temperature readings of air coming out of cabin vents (where AC cold air comes from).
2) Gauges connected to both high and low side. Connect gauges first, then switch on the AC so that pressure change behaviour can be monitored.
3) Cabin blower fan: full speed
4) Switch AC on and watch what happens with gauge needles. This is why its ideal to be making a short video.
5) Watch for speed of AC condenser fan/radiator fan. Do they switch b/w slow speed and high speed etc..
6) At 1500rpm let the system stabilise for approx 5-10 mins and then note the pressures. Now this is the actual step. All before this was preparation for this.
7) After 10 mins of AC operation note the cabin vent air temperature. Put the probe a few centimetres inside the vent, don't keep it in front of vent.
mota mota yehi hai. baqi experts can tell you if there's something that needs doing differently than what I've put here.
No I've just begun considering those two ideas. No clue about costs. I don't even know where I'll buy them from. But I think the anti-uv film should be available from reputable car decoration shops that sell tinted films.
As for roof insulation, I'm thinking either of two materials locally known as 'namda' (a soft raw wool/cotton -ish carpet underlay), or that closed-cell foam underlay (jumbolon type) - both being available at carpet shops. Still undecided which one can stop heat better. Any ideas?
