Hello again Matias,
I know nil about the Thierrymin, so cannot comment either way.. But at least you would have Thierry on hand to give help / advice if its needed, and component tolerances aren't critical as I understand it, so it could be a good choice.
Not knowing what parts are easily available to you does make advice difficult but lets go over the basics.. You need two high frequency oscillators >100kHz and <1MHz I would say. At least one of these oscillators needs to be tunable in some way. You can make a really crap 'theremin' using RC oscillators - in fact, you can make one with a couple of CMOS gates, resistors and capacitors, but I wouldn't bother!
However - in terms of simplicity, avoiding inductors does make life easier! You only need a couple of cheap unbuffered CMOS inverters, and tuning is performed with simple variable resistor - I suspect you could get the parts for this in any country http://www.theremin.us/100/minimum.html
But if you can get all the components for the Thierrymin, then this is likely to be better.
If you can get 455kHz IF transformers, then I would be inclined to point you in the direction of using these with simple CMOS oscillators and use my adjustable antenna for tuning.. In fact, this tuning scheme is IMO the easiest to implement for all simple theremins as it removes any need for electronic tuning.. its far easier to tune than a telescopic antenna, and could be used with the Thierrymin.
I used aluminium tube into which the studding fitted (- as tightly as possible, but you need to be able to push the studding into the tube over its whole length.. I then put the tube with studding inside it into a vice, and squeezed the tube so the studding 'cut' (more like squashed) a thread into the tube.
When this is done, firmly fix the stud to the theremin, and by rotating the tube on can finely increase or decrease the length of the antenna.
I would make the stud and tube lengths about 45cm, about 2cm of the stud is used to secure it to the theremin, and the effective antenna length can be adjusted from 45cm (tube fully down) to about 80cm (tube fully up) .. Set the tube to mid position (top of tune ~60cm above theremin), tune the electronics, and one has fine tuning control by slight rotation of the tube, but can cater for almost any variation in environment.
The tube I used had an inner diameter that accepted M6 stud.. But none of this is critical, length and diameter can be adjusted to taste.. I just like long thin antennas! ;-)
This picture shows one (nearest) of my 16 pitch only theremins which used this tuning method at the Royal Festival Hall (2010)
And a close-up of the antenna:
Really, the first thing we need to know is what parts you can get! - Do you have a local supplier on the WWW so we can view their catalog if you post a link here ?
Knowing whats available to you would be a big help.
Fred.
found http://www.electrocomponentes.com/pdf/Catalogo_web.pdf which has transistors pots passives CMOS but doesnt seem to have IFTs or inductors
Also looks like RS components has a distribution network in Argentina, and seems to stock nearly everything - but I cant find trimmable inductors or IFT's .. Can find Bourns 6300 series though ;-)
Digikey ships to Argentina for $40
And Mouser seems to be local
Hell, looks like you can get any part you need!