Dear friend
Once you are invested in the Brown Scapular, you are invested in it. So if you lose the Brown Scapular, you do not wear it for a period, your Brown Scapular breaks and you need to get another one and for some period you wear none, you are still invested in the Brown Scapular. The Blessing is upon yourself and the Brown Scapular is an outward sign of the inward devotion and investiture, an outward sign of your blessing and pledge of salvation.
So if you now desire to wear once again, the Brown Scapular, just get one and wear it.
You do not have to be a Lay Carmelite to wear a Brown Scapular, you can hold a devotion to the Brown Scapular without professing as a Lay Third Order Carmelite and a nice bonus to this is that you share in the prayer of those invested in the Brown Scapular, that being the order to which it belongs, the Carmelites. Very nice bonus indeed
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I hope that helps
By the way our late Pontiff, Pope John Paul II was invested in the Brown Scapular and was a Lay Third Order Carmelite.
God Bless you and much love and peace to you
Teresa