You can join PTG from anywhere in the world but PTG is officially only in Canada, USA and Mexico. It only has chapters, (local organizations) in Canada and Mexico. You need to see the website: www.ptg.org
The application fee is $150 and then the annual dues (you must pay every year to retain membership)are a little more than $200, depending on which Chapter you become assigned to or choose to join. When you join, you become an Associate Member. As an Associate Member, you will be able to purchase the PACE program materials which are a good guide for study.
About the only way you can take the RPT Exams is to travel to the USA or Canada to take them. There are some exams offered at East Coast Regional Seminars but you need to be sure they are offered, pay the registration fee for the seminar and the exam fees in advance. The total exam fees are presently $180 but they are likely to double next week when the PTG Council votes to make them $360.
The sum of all those expenses including an airplane trip and lodging will run into the Thousands of dollars. But if PTG RPT accreditation is your only way to show proof that you have basic professional skills, it will be one way to get them that otherwise is not available in your country. You just have to decide how much it is worth it to you.
If you come to the USA to take the exams, you will want to be very sure that you can pass them. It sounds like you could pass the tuning exam but you may need some study to pass the technical exam. There is a written exam required first. Even it may be a problem because, of course, it is in English, using American terminology (which often differs from that used in England). There is a book available from PTG which is not very expensive which has all of the specific names for piano parts and functions. It is called, "Piano Parts and Their Functions".
I have heard of training programs in Germany but that may be an even worse language barrier for you. It may also cost more than it would in North America.
I still recommend you contact PTG whether you can afford membership or not. As a person from Europe, they may allow you to purchase the PACE program materials, I am not sure. The person you should write to is Sandy Roady and her e-mail is: firstname.lastname@example.org I must say, however that Sandy will be very busy the next two weeks because of the PTG Annual Convention which will be in California. She does answer her e-mail promptly, however and can do it from her location at the Convention.
You may also see my website for information on Tuning. The "Articles" tab has information about Tuning intended to help those who wish to pass the PTG Tuning Exam. New information will be available soon, so keep looking there from time to time: www.billbremmer.com
Good luck in your endeavor!