My son is also in Grade 10 now and will be either going into the
International Schools or JCs when we return to Singapore this year. However he will not be required to take J-Pact as it is only for international students.
There will not be J-PACT books available as not many students will be taking it. You may want to get some Secondary 4 assessment books to try out. Most of the assessment books have end of the year assessments and if yu are able to handle all these, I think you should be fine. These books are available online at
www.popular.com.sg so you don't need to fly in to buy.
I find that the better publisher for Mathematics books is Shinglee Publishers.