There must be a lot of ways you can get these seeds. Either you buy fresh jalapeños from you local supermarket and then collect the seeds or you order them online from a chili-pepper vendor. A quick Google search should get you there.
I saw you are from India. Here from Amazon (India), they sell the seeds. https://www.amazon.in/Nelesa-Gardening-Jalapeno-Capsicum-Vegetable/dp/B00IRZNWZU
Jalapeno pepper might have different varieties. You should check it out to see which variety is most suitable for your research.